feat(workspace): add TOOLS.md, BOOTSTRAP.md, and disk-to-DB import (#477)

* feat(workspace): add TOOLS.md, BOOTSTRAP.md, and disk-to-DB import

Add two new OpenClaw-compatible workspace markdown files:

- TOOLS.md: Environment-specific tool notes (SSH hosts, device names,
  etc.) injected into the system prompt under "## Tool Notes". Seeded
  as comment-only (like HEARTBEAT.md) so it's effectively empty until
  the user adds real content. Not write-protected — the agent can
  update it as it learns the environment.

- BOOTSTRAP.md: First-run onboarding ritual. Injected FIRST in the
  system prompt when present. Guides the agent through introducing
  itself, learning about the user, and updating workspace files.
  Only seeded on truly fresh workspaces (no existing identity files)
  to avoid triggering the ritual on existing deployments. Agent clears
  it via `memory_write(target="bootstrap")` when done.

Add `Workspace::import_from_directory()` for disk-to-DB import:

- Scans a directory for *.md files and imports any that don't already
  exist in the database (never overwrites user edits)
- Controlled by WORKSPACE_IMPORT_DIR env var, runs after seed_if_empty()
- Enables Docker images / deployment scripts to ship customized
  workspace templates that override generic seeds
- Backwards compatible: no-op when env var is unset

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

* fix: address PR review comments

- Use stable `path.extension() != Some(OsStr::new("md"))` instead of
  unstable `is_none_or` (nightly-only)
- Use `tokio::join!` for concurrent DB reads in fresh-workspace check
- Skip unreadable directory entries instead of failing the entire import
- Skip unreadable files instead of failing the entire import

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <[email protected]>

src/error.rs

@@ -331,6 +331,9 @@ pub enum WorkspaceError {
 
     #[error("Heartbeat error: {reason}")]
     HeartbeatError { reason: String },
+
+    #[error("I/O error: {reason}")]
+    IoError { reason: String },
 }
 
 /// Orchestrator errors (internal API, container management).