fix(paired): bound arbiter interventions to stop infinite arbiter loop

The owner↔reviewer↔arbiter loop could repeat forever: when the arbiter
ruled PROCEED/REVISE/RESET it reset round_trip_count to 0, and nothing
tracked how many times the arbiter had already intervened. A re-deadlock
re-invoked the arbiter without bound.

Add a persistent arbiter_intervention_count (new column + migration 020)
that survives the round-trip reset, and a configurable cap
ARBITER_MAX_INTERVENTIONS (default 1). Once the arbiter has intervened
that many times and the loop still deadlocks, requestArbiterOrEscalate
escalates straight to the user instead of re-invoking the arbiter.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/paired-execution-context-reviewer.ts

@@ -193,6 +193,7 @@ export function handleReviewerCompletion(args: {
         arbiterLogMessage,
         escalateLogMessage,
         logContext: { taskId, verdict, summary: summary?.slice(0, 100) },
+        arbiterInterventionCount: task.arbiter_intervention_count ?? 0,
       });
       return;
     }