feat(app): group projects by repository with teammate channel sections

[iamnbutler]

Part of #15 (tracked by #58); a dogfooding gap from #5.

Behavior

• Projects with a GitHub remote are identified by repository, compared case-insensitively, so all their checkouts form one project. Other Git folders stay identified by host and checkout. Client navigation only.
• Creating channels and Archive inactive use this host's first known checkout. Projects checked out only on teammates' hosts name those hosts and can't start channels here. Cmd+O only adds a project.
• Sidebar order: Channels (mine), each teammate's section with a folded <name> · Archived section, then my Inactive and Archived. Delete is offered only for this host's rows.
• All Projects shows one section per project. Old saved selections, Dashboard drafts, and Issues/PRs filters keep working.

Validation

• bun types, bun run ci, and React Doctor pass (only the App complexity warning, which already exists and is now lower).
• bun desktop build dev builds; the app wasn't launched.
• Headless Chromium drove the real app on an isolated source host with real clones githubnext/ace2 and GitHubNext/ACE2:
  • Open/Cmd+O added projects without creating channels.
  • Channels were created in the first checkout.
  • The picker and All Projects showed one ace2 project.
  • Old [host, path] selections reopened the expected channels.
  • Drafts and Closed filters survived a reload.
  • Archive and delete worked.
  • With only the browser clock set 7h ahead (no real aging, host listings unchanged, no peer), Inactive folded and Archive inactive archived only the first checkout.
• Disposable data only; no page errors; processes and ports cleaned up.

Limitations

• Native UI isn't validated: the macOS session is locked.
• No second person or host is available; that check is deferred to tomorrow (Verify Ace with two machines on the tailnet #10).
• Two clones on one host: channels go to the first, and Archive inactive skips the other's.
• Non-Git folders can't start channels; this was already the case (Opening a non-Git folder adds a project that cannot start channels #162).

Built in Ace

Implementation, checks, build, browser validation, and GitHub updates were done in an Ace channel. Outside Ace:

• Coordination and review: Codex coordinated the work and reviewed the code and PR (Run and resume Codex and Claude Code in Ace channels #9, Wake waiting agents on channel handoffs instead of blocking in shell polling loops #108, Let agents supervise and follow up with subagents #52).
• Browser: an ad-hoc Playwright script stood in for Ace browser tooling (Inspect and debug browser pages from an Ace channel #50).
• Screenshots: Codex viewed the screenshots because the channel's read rejects PNGs (Let native agents inspect image files by path #51).