fix: bounded audit loop (deterministic gates only, 3 pushbacks, escalate)

Audit loop engine (cloud/audit_loop.py): Finding/PushbackPacket/LoopState pure functions; deterministic gates only, subjective -> needs_review; packet completeness enforced; standards-weakening -> escalate; regression and missing-gate checks enforce full re-run; MAX_PUSHBACKS=3, round>=3 -> escalate. Persistence in new single-row task_audit_loop_state (attempts DDL pattern: module CREATE_TABLE_SQL + db.py POSTGRES_SCHEMA + migrations list + server init + worker ensure); task_attempts NOT reused (attempt_no PK collision) and task_followups NOT reused (user messages). Worker.audit_loop_evaluate is the explicit opt-in hook (task audit_loop field only, no env switch, never called by run_one); escalate audits worker_audit_loop_escalated; corrupted/missing count fail-closes to escalate.

cloud/migrations.py

@@ -89,6 +89,8 @@ MIGRATION_TABLES = (
     "resident_polls",
     # 尝试账本（v6）：同款复合主键、无身份列。
     "task_attempts",
+    # 审计循环状态（audit loop）：task_id 单行主键、无身份列。
+    "task_audit_loop_state",
 )
 
 _SKIP_TABLES = frozenset({"kb_fts", "sqlite_sequence"})