Brightencode Launcher v0.1.20

Add Installed/My Apps/Browse tabs with catalog search

The launcher was single-purpose (just the installed-apps gallery) —
this adds a tab bar plus a search input above the gallery so the
whole catalog is browsable from inside the app, not just the website:

- browse_catalog (orchestrator::search_catalog, worker's GET /search)
  lists the public catalog, cross-referenced against the local library
  so each tile shows Install vs Launch. Utility repos are filtered out,
  matching securexe-web's own Library page default.
- install_from_catalog reuses flow::install_and_launch exactly like a
  signed securexe://run link or the in-app Update action — no
  signature needed since the user is installing something already
  sitting in their own launcher, not following an arbitrary link.
- repo::is_safe_repo_path validates a Browse-tile repo string arriving
  over IPC (from the worker's own search results) before it's turned
  into a filesystem slug.
- My Apps tab is a stub for now (cross-device library sync isn't wired
  up yet) — shows an explicit "coming soon" empty state rather than an
  empty gallery that looks broken.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>