fix: prevent infinite loops in paired review (merge_ready oscillation, arbiter re-invocation)

- Owner finalize with concerns now checks deadlock threshold before
  looping back — prevents merge_ready ↔ active infinite oscillation
- Arbiter verdict resets round_trip to threshold-1 instead of 0,
  giving agents one round before re-triggering arbiter

src/db.ts

@@ -668,9 +668,7 @@ function createSchema(database: Database): void {
 
   // Migration: add completion_reason column to paired_tasks if it doesn't exist
   try {
-    database.exec(
-      `ALTER TABLE paired_tasks ADD COLUMN completion_reason TEXT`,
-    );
+    database.exec(`ALTER TABLE paired_tasks ADD COLUMN completion_reason TEXT`);
   } catch {
     /* column already exists */
   }