feat: groupes de travail (P5)

Ajoute la notion de groupe — collection nommée de repos (membership légère
persistée, many-to-many) — pour piloter plusieurs repos en simultané :

- DB : migration #5 (tables groups + group_repos, FK ON DELETE CASCADE).
- GroupManager (synchrone, EventEmitter) + routes REST /api/v1/groups ;
  ne persiste que la membership, worktrees/sessions filtrés par repoId côté client.
- Protocole : GroupSummary, DTOs, topic WS « groups », events group_update/removed
  (additifs, PROTOCOL_VERSION inchangé).
- Web : store groups, GroupsListView, GroupView (réutilise RepoSection),
  grille multi-terminaux (TerminalGrid/TerminalCell), action « feature cross-repo »
  (orchestration client, tolérante aux échecs partiels), routes + i18n EN/FR.
- Tests : group-manager.test.ts + extension protocol.test.ts ; acceptance-p5.mjs.

packages/shared/test/protocol.test.ts

@@ -62,7 +62,7 @@ function assertInvariants(msg: ClientMessage): void {
       expect(msg.bytes).toBeGreaterThanOrEqual(0);
       break;
     case 'sub':
-      expect(msg.topics.every((t) => t === 'sessions')).toBe(true);
+      expect(msg.topics.every((t) => t === 'sessions' || t === 'worktrees' || t === 'groups')).toBe(true);
       break;
     case 'ping':
       break;
@@ -117,9 +117,14 @@ describe('parseClientMessage — cas valides', () => {
     expect(parseClientMessage('{"type":"ack","channel":1,"bytes":0}')).toEqual({ type: 'ack', channel: 1, bytes: 0 });
   });
 
-  it('sub avec topics sessions/worktrees (et tableau vide accepté)', () => {
+  it('sub avec topics sessions/worktrees/groups (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":["groups"]}')).toEqual({ type: 'sub', topics: ['groups'] });
+    expect(parseClientMessage('{"type":"sub","topics":["sessions","worktrees","groups"]}')).toEqual({
+      type: 'sub',
+      topics: ['sessions', 'worktrees', 'groups'],
+    });
     expect(parseClientMessage('{"type":"sub","topics":[]}')).toEqual({ type: 'sub', topics: [] });
   });