Support custom commands and workspace launches in the command palette

[khoi]

Summary

• Problem: the command palette had no path for user-defined commands or repeatable workspace launches from supaterm.json
• Why it matters: users could not define reusable project commands or recreate named terminal layouts from the palette
• What changed: added shared custom-command models and schema generation, global plus nearest-local command loading and merge rules, palette integration for resolved custom rows, and host-owned execution for simple commands plus workspace launches
• What did NOT change (scope boundary): no browser panes, no mixed surface layouts, and no new socket-facing workspace request surface

Rationale

This keeps config discovery, path resolution, merge precedence, environment validation, and workspace sequencing inside one terminal-owned boundary instead of leaking those rules into the palette reducer. The host already had the right space and split-tree primitives, so the cleanest forward path was to compose those directly rather than add another orchestration layer.

User-visible / Behavior Changes

• Users can define custom command palette entries in supaterm.json
• Simple custom commands run in the focused pane
• Workspace commands can create or focus a named space and materialize tabs plus panes with titles, cwd, startup commands, and environment variables
• The palette now shows custom-command load problems without breaking built-in actions

Diagram (if applicable)

Before:
[cmd-p] -> [built-in rows only] -> [no user-defined execution path]

After:
[cmd-p] -> [built-ins + resolved custom rows]
         -> [select custom command]
         -> [host loads/merges config]
         -> [run in focused pane OR recreate/focus workspace]

Human Verification

• Verified scenarios:
  • ran focused mac tests for the custom-command catalog and palette reducer paths
  • push hooks passed make web-check and the full mac xcodebuild test suite after rebasing onto main
• Edge cases checked:
  • nearest-local config overrides global by id
  • reserved environment keys are rejected
  • recreate confirmation flow still routes through the existing confirmation path
• What you did not verify:
  • no live manual app run of cmd-p with a hand-authored supaterm.json in this rebased pass
• How can a human manually verify this:
  • create a supaterm.json with one simple command and one workspace command in a project directory
  • launch the app, focus a pane in that directory, press cmd-p, and run the custom entries
  • confirm the simple command writes into the focused pane and the workspace command recreates or focuses the named space with the expected layout

[khoi]

Closing all open PRs per request.