Turn autotile on, which is what makes placement automatic

COSMIC ships autotile off, so every new window opened floating at whatever
size the application asked for, on top of whatever you were looking at. The
key already existed in cosmic-conf's registry and had simply never been set.

Gaps come with it. They are invisible until windows tile -- with nothing being
laid out, nothing has a gap -- so setting one without the other is half a
change. gaps_out is doubled so the screen edge reads as margin rather than as
one more seam.

autotile_behavior is deliberately not a conf key. It defaults to Global, which
retiles workspaces that already exist rather than only arming new ones, and
that is the value worth having; anyone who wants PerWorkspace can set it in
cosmic-settings without this file overwriting them.

config/cosmic.conf

@@ -20,6 +20,35 @@
 
 $mainMod = SUPER
 
+# --- Tiling -------------------------------------------------------------
+#
+# COSMIC ships with autotile off, so a new window opens floating, at whatever
+# size the application asked for, on top of what you were already looking at.
+# This is the setting that makes window placement automatic: each new window
+# takes a share of the screen instead.
+#
+# It applies immediately and everywhere. `autotile_behavior` is a separate
+# COSMIC key that defaults to Global, which retiles workspaces that already
+# exist; the other value, PerWorkspace, arms only workspaces created from now
+# on. There is no conf key for it because the default is the one worth having
+# -- if you want the other, set it in cosmic-settings and this file will not
+# fight you over it.
+#
+# Super+Y still toggles tiling for the current workspace on its own, so a
+# workspace you want to keep floating does not need this turned off.
+#
+# Gaps are here rather than in the theme block because they are only visible
+# once windows tile: with autotile off nothing is laid out, so nothing has a
+# gap. gaps_out is doubled so the screen edge reads as deliberate margin
+# rather than as one more seam.
+$gap = 4
+
+general {
+    autotile = true
+    gaps_in  = $gap
+    gaps_out = $gap * 2
+}
+
 # --- Launcher -----------------------------------------------------------
 #
 # The hyprcosmic profile does not start cosmic-launcher or cosmic-app-library,