fix(paired): cap consecutive reviewer silent-failure retries

The reviewer (codex) sometimes emits a final result with no visible text.
The runtime marks the run failed → handleFailedReviewerExecution
preserves status as review_ready → the follow-up scheduler re-queues
another reviewer-turn → loop. The existing round_trip / arbiter caps
never fire because round_trip_count only advances on owner-side
submissions; bot-side reviewer flakes never increment it.

Mirror the owner_failure_count pattern: add reviewer_failure_count to
paired_tasks, increment on each silent failure, and escalate via
requestArbiterOrEscalate once it reaches 2. Reset to 0 on every
successful reviewer completion path (PROCEED/REVISE/arbiter/wait-for-user)
and when the owner re-submits a fresh review cycle.

Repro chat: 1507762222724546560 (stock-adiviser). Task
33968d31-0da2-480c-85d3-7a3999822ab4 logged 11 consecutive
reviewer-turn entries with no work_items and round_trip_count stuck
at 1.

src/db/base-schema.ts

@@ -121,6 +121,7 @@ export function applyBaseSchema(database: Database): void {
       review_requested_at TEXT,
       round_trip_count INTEGER NOT NULL DEFAULT 0,
       owner_failure_count INTEGER NOT NULL DEFAULT 0,
+      reviewer_failure_count INTEGER NOT NULL DEFAULT 0,
       owner_step_done_streak INTEGER NOT NULL DEFAULT 0,
       finalize_step_done_count INTEGER NOT NULL DEFAULT 0,
       task_done_then_user_reopen_count INTEGER NOT NULL DEFAULT 0,