feat: auto-trigger reviewer after owner completion with round trip limit

- Owner finishes → auto mark review_ready → reviewer executes
- Reviewer finishes → task back to active → owner can respond
- Automatic ping-pong until consensus or round trip limit
- PAIRED_MAX_ROUND_TRIPS env var (default 10, 0 = unlimited)
- round_trip_count tracked per task in DB

src/db.test.ts

@@ -556,7 +556,7 @@ describe('paired task state', () => {
       reviewer_service_id: 'codex-review',
       title: 'wire up workspaces',
       source_ref: 'HEAD',
-      plan_notes: null,
+      plan_notes: null, round_trip_count: 0,
       review_requested_at: null,
       status: 'active',
       created_at: '2026-03-28T00:00:00.000Z',
@@ -594,7 +594,7 @@ describe('paired task state', () => {
       reviewer_service_id: 'codex-review',
       title: null,
       source_ref: null,
-      plan_notes: null,
+      plan_notes: null, round_trip_count: 0,
       review_requested_at: null,
       status: 'active',
       created_at: '2026-03-28T00:00:00.000Z',