Give rofi a theme, in four layers

`rofi -show drun` came up unstyled. Three separate reasons, all of them
invisible: `import-theme` wrote ~/.config/rofi/theme.rasi, but rofi only ever
auto-loads config.rasi and nothing imported theme.rasi; theme.rasi holds a
HyDE palette and nothing else, no widget geometry at all; and no layout was
shipped anywhere for it to colour.

The layering mirrors what config/waybar already does, for the same reason --
a theme supplies colours, and the layout has to survive being handed a theme
that defines only some of them:

  1. palette.rasi   defaults, under the exact names HyDE themes use
  2. theme.rasi     the installed theme's rofi.theme, written by cosmic-conf
  3. rules.rasi     geometry and layout, with no colour literals at all
  4. local.rasi     per-machine paths: sidebar wallpaper, icon theme

Later imports win, so a theme recolours the launcher without rules.rasi
knowing a theme exists, and a machine points at its own wallpaper without
either of them knowing the path. Unlike waybar there is no bridge step: a HyDE
rofi.theme defines the names rules.rasi already references.

1 and 3 are shared and go under /usr/share/hyprcosmic/rofi. 2 and 4 must be
per-user, and config.rasi with them: it imports those two relatively, and rofi
resolves a relative @import against the importing file's directory.

rules.rasi is HyDE's style_1 with three deliberate departures, documented in
its header. HyDE computes the border width, radius and font in rofilaunch.sh
before invoking rofi; there is no launcher script here -- the keybinding runs
`rofi -show drun` bare -- so those are baked in. The sidebar image moves to
local.rasi because HyDE's ~/.cache/hyde/wall.thmb does not exist outside HyDE.
And dummywall gets `background-color: @main-bg` rather than transparent, so a
machine with no wallpaper set shows a panel instead of a hole.

The display-* labels are Nerd Font glyphs copied byte-for-byte out of
style_1.rasi. They are Private Use Area codepoints and do not survive being
retyped; verified as U+F303, U+F120, U+F07B, U+F2D0, each followed by a thin
space, and confirmed present in JetBrainsMono Nerd Font via
`fc-list :charset=`.

Verified with `rofi -dump-theme` and `-dump-config`: both exit 0 with empty
stderr, and the merged dump shows the Tokyo Night theme's main-bg beating the
palette default.

config/rofi/config.rasi

@@ -0,0 +1,50 @@
+/* rofi configuration and theme entry point for a HyprCosmic session.
+ *
+ * Below the configuration block this file is only an import list, because the
+ * order is the whole design:
+ *
+ *   1. palette.rasi   default colours, under the names HyDE themes use
+ *   2. theme.rasi     the installed HyDE theme's rofi.theme, if any
+ *   3. rules.rasi     geometry and layout; no colour literals at all
+ *   4. local.rasi     per-machine bits: the sidebar wallpaper, the icon theme
+ *
+ * Imports are read strictly in sequence and a later definition of a property
+ * wins over an earlier one. That is what lets step 2 recolour the launcher
+ * without step 3 knowing a theme exists, and step 4 point at a wallpaper
+ * without either of them knowing the path.
+ *
+ * There is no bridge step, unlike waybar: a HyDE rofi.theme defines exactly the
+ * names rules.rasi already references, so nothing needs mapping.
+ *
+ * Steps 2 and 4 are relative imports, which rofi resolves against the directory
+ * of the importing file. That is why this file belongs at
+ * ~/.config/rofi/config.rasi rather than under /usr/share: both are per-user.
+ * It is also the only name rofi loads on its own, so `rofi -show drun` from a
+ * keybinding picks all of this up with no arguments and no launcher script.
+ *
+ * Both relative imports must exist. A missing @import is an error rofi reports
+ * in place of the launcher, not a warning it skips, so `cosmic-conf` writes
+ * theme.rasi and local.rasi even when there is nothing to put in them -- empty,
+ * in which case the defaults from step 1 stand.
+ */
+
+configuration {
+    modi:                "drun,run,window,filebrowser";
+    show-icons:          true;
+
+    /* Nerd Font glyphs, as HyDE's style_1 has them: apps, terminal, files,
+     * windows. They render as tofu without a Nerd Font installed; see the font
+     * list in rules.rasi. */
+    display-drun:        " ";
+    display-run:         " ";
+    display-filebrowser: " ";
+    display-window:      " ";
+
+    drun-display-format: "{name}";
+    window-format:       "{w}{t}";
+}
+
+@import "/usr/share/hyprcosmic/rofi/palette.rasi"
+@import "theme.rasi"
+@import "/usr/share/hyprcosmic/rofi/rules.rasi"
+@import "local.rasi"

config/rofi/palette.rasi

@@ -0,0 +1,31 @@
+/* Default colours for the HyprCosmic launcher.
+ *
+ * Only one name set is needed here, unlike waybar's palette.css. A HyDE theme's
+ * rofi.theme is a list of exactly these names -- main-bg, select-fg and so on --
+ * and rules.rasi references the same names directly, so there is nothing to
+ * bridge between. Importing a theme after this file simply re-points them.
+ *
+ * Defining them here is what makes a missing theme harmless: rules.rasi always
+ * resolves against something, so an unthemed launcher renders with these values
+ * instead of every widget falling back to rofi's stock grey.
+ *
+ * Values are Tokyo Night, matching cosmic-conf's own defaults.
+ */
+
+* {
+    /* Window and text. main-br is the window border, main-ex an accent HyDE
+     * uses for secondary text; rofi themes vary in how much of it they set. */
+    main-bg:         #1a1b26e6;
+    main-fg:         #c0caf5ff;
+    main-br:         #bb9af7ff;
+    main-ex:         #7dcfffff;
+
+    /* The highlighted row. */
+    select-bg:       #7aa2f7ff;
+    select-fg:       #1a1b26ff;
+
+    /* Named by HyDE's themes but unused by this layout. Defined so a theme that
+     * sets them parses, and so one that does not still resolves. */
+    separatorcolor:  transparent;
+    border-color:    transparent;
+}

config/rofi/rules.rasi

@@ -0,0 +1,173 @@
+/* Geometry and layout for the HyprCosmic launcher.
+ *
+ * Adapted from HyDE's style_1 ("Background image with a sidebar list"), which
+ * is the layout its rofilaunch.sh uses by default. Two deliberate differences:
+ *
+ *   - HyDE injects the border radii, border width and font at the command line,
+ *     as three -theme-str arguments computed from Hyprland's own gaps and
+ *     border settings. We have no launcher script -- the keybinding in
+ *     cosmic.conf runs plain `rofi -show drun` -- so those values are written
+ *     out here, at the defaults rofilaunch.sh would have produced.
+ *   - The sidebar image lives in local.rasi rather than here, because the
+ *     wallpaper path is per-user. HyDE points at ~/.cache/hyde/wall.thmb, a
+ *     thumbnail its wallpaper scripts generate; we do not run those, so
+ *     pointing there would render an empty panel on every machine.
+ *
+ * No colour literals: every colour is a name from palette.rasi, which a theme
+ * may have re-pointed. That separation is what lets `cosmic-conf import-theme`
+ * recolour the launcher without touching a line of layout.
+ */
+
+/* Pango takes a comma-separated family list, so the Nerd Font is a preference
+ * rather than a requirement -- the glyphs in config.rasi's mode labels need it,
+ * but everything else still renders without it. */
+* {
+    font: "JetBrainsMono Nerd Font, Noto Sans Mono 10";
+}
+
+
+// Main //
+window {
+    height:                      33em;
+    width:                       63em;
+    transparency:                "real";
+    fullscreen:                  false;
+    enabled:                     true;
+    cursor:                      "default";
+    spacing:                     0em;
+    padding:                     0em;
+    border:                      2px;
+    border-radius:               30px;
+    border-color:                @main-br;
+    background-color:            @main-bg;
+}
+mainbox {
+    enabled:                     true;
+    spacing:                     0em;
+    padding:                     0em;
+    orientation:                 horizontal;
+    children:                    [ "dummywall" , "listbox" ];
+    background-color:            transparent;
+}
+
+/* The sidebar. Solid colour here so that a machine with no wallpaper override
+ * gets a panel in the theme's own background, not a hole. local.rasi paints an
+ * image over the top when there is one. */
+dummywall {
+    spacing:                     0em;
+    padding:                     0em;
+    width:                       37em;
+    expand:                      false;
+    orientation:                 horizontal;
+    children:                    [ "mode-switcher" , "inputbar" ];
+    background-color:            @main-bg;
+}
+
+
+// Modes //
+mode-switcher {
+    orientation:                 vertical;
+    enabled:                     true;
+    width:                       3.8em;
+    padding:                     9.2em 0.5em 9.2em 0.5em;
+    spacing:                     1.2em;
+    background-color:            transparent;
+}
+button {
+    cursor:                      pointer;
+    border-radius:               2em;
+    background-color:            @main-bg;
+    text-color:                  @main-fg;
+}
+button selected {
+    background-color:            @main-fg;
+    text-color:                  @main-bg;
+}
+
+
+// Inputs //
+/* The entry is hidden: typing filters the list without a visible prompt, which
+ * is what gives style_1 its uncluttered look. inputbar still has to exist for
+ * keystrokes to reach the filter. */
+inputbar {
+    enabled:                     true;
+    children:                    [ "entry" ];
+    background-color:            transparent;
+}
+entry {
+    enabled:                     false;
+}
+
+
+// Lists //
+listbox {
+    spacing:                     0em;
+    padding:                     2em;
+    children:                    [ "dummy" , "listview" , "dummy" ];
+    background-color:            transparent;
+}
+listview {
+    enabled:                     true;
+    spacing:                     0em;
+    padding:                     0em;
+    columns:                     1;
+    lines:                       8;
+    cycle:                       true;
+    dynamic:                     true;
+    scrollbar:                   false;
+    layout:                      vertical;
+    reverse:                     false;
+    expand:                      false;
+    fixed-height:                true;
+    fixed-columns:               true;
+    cursor:                      "default";
+    background-color:            transparent;
+    text-color:                  @main-fg;
+}
+dummy {
+    background-color:            transparent;
+}
+
+
+// Elements //
+element {
+    enabled:                     true;
+    spacing:                     0.8em;
+    padding:                     0.4em 0.4em 0.4em 1.5em;
+    border-radius:               20px;
+    cursor:                      pointer;
+    background-color:            transparent;
+    text-color:                  @main-fg;
+}
+element selected.normal {
+    background-color:            @select-bg;
+    text-color:                  @select-fg;
+}
+element-icon {
+    size:                        2.8em;
+    cursor:                      inherit;
+    background-color:            transparent;
+    text-color:                  inherit;
+}
+element-text {
+    vertical-align:              0.5;
+    horizontal-align:            0.0;
+    cursor:                      inherit;
+    background-color:            transparent;
+    text-color:                  inherit;
+}
+
+
+// Error message //
+error-message {
+    text-color:                  @main-fg;
+    background-color:            @main-bg;
+    text-transform:              capitalize;
+    children:                    [ "textbox" ];
+}
+textbox {
+    text-color:                  inherit;
+    background-color:            inherit;
+    vertical-align:              0.5;
+    horizontal-align:            0.5;
+}