P3-A: worktrees multi-repo & cycle de vie (backend)

Enregistrement de repos et gestion de leurs worktrees git, source de vérité
= git (worktrees dérivés + cache court par repo), corrélation worktree ↔
sessions par cwd, mutations sérialisées par repo.

- shared: RepoSummary, PostCreateHook, WorktreeSummary, WorktreeGitStatus ;
  messages WS repo_update/worktree_update/*_removed ; topic sub 'worktrees'
  (+ parseClientMessage) ; DTOs REST repos/worktrees.
- db: migration id:3 (table repos).
- core/git.ts: couche git sûre (execFile, jamais de shell, -- avant chemins,
  GIT_OPTIONAL_LOCKS=0), parseWorktreePorcelain, list/add/remove/prune/status/
  ahead-behind, validation branche + chemin.
- core/claude-trust.ts: pré-trust atomique de ~/.claude.json (spike S3).
- core/worktree-manager.ts: repos CRUD, create (worktree add + pré-trust +
  hooks post-create + startSession optionnel), adopt, delete (garde-fous 409
  dirty / 400 main / 409 session live), prune ; events.
- routes/repos.ts + routes/worktrees.ts, câblage app.ts, gateway topic worktrees.
- tests: git (repos tmp réels), claude-trust, worktree-manager (146 verts).

packages/shared/test/protocol.test.ts

@@ -96,8 +96,9 @@ describe('parseClientMessage — cas valides', () => {
     expect(parseClientMessage('{"type":"ack","channel":1,"bytes":0}')).toEqual({ type: 'ack', channel: 1, bytes: 0 });
   });
 
-  it('sub avec topics sessions (et tableau vide accepté)', () => {
+  it('sub avec topics sessions/worktrees (et tableau vide accepté)', () => {
     expect(parseClientMessage('{"type":"sub","topics":["sessions"]}')).toEqual({ type: 'sub', topics: ['sessions'] });
+    expect(parseClientMessage('{"type":"sub","topics":["sessions","worktrees"]}')).toEqual({ type: 'sub', topics: ['sessions', 'worktrees'] });
     expect(parseClientMessage('{"type":"sub","topics":[]}')).toEqual({ type: 'sub', topics: [] });
   });