feat: unify 3 bot services into single process

- Add UNIFIED_MODE flag (default on, disable with UNIFIED_MODE=0)
- Register all 3 Discord bots in one process (claude, codex, review)
- Load all registered groups regardless of agent_type (codex/owner priority)
- Start credential proxy and container cleanup at unified startup
- shouldServiceProcessChat returns true in unified mode
- Add findChannelByName for role-based response routing
- Backward compatible: UNIFIED_MODE=0 restores per-service behavior

src/db.test.ts

@@ -607,13 +607,6 @@ describe('paired task state', () => {
       updated_at: '2026-03-28T00:10:00.000Z',
     });
 
-    expect(getPairedTaskById('paired-task-2')?.gate_turn_kind).toBe(
-      'implementation_start',
-    );
-    expect(getPairedTaskById('paired-task-2')?.reviewer_verdict).toBe(
-      'done_with_concerns',
-    );
-
     upsertPairedWorkspace({
       id: 'paired-task-2:reviewer',
       task_id: 'paired-task-2',