feat(db,contracts): W5-C subscription units migration 0025, contracts and mapping

- subscription: status pending (TMDB not ready: searchable/evaluable, not completable),
  last_searched_at / next_search_at
- content_unit (season): episode_total ledger with source / lock / timestamp
- acquisition_plan: unit_keys (Slot × unit reservation) and file_selection; drop the
  one-in-flight-per-slot unique index (checked under slot row lock per unit instead)
- new tables slot_deferral, slot_unit (per-unit quality ledger), subscription_history
- contracts: SubscriptionParams, SubscriptionHistory, SlotDeferral, SlotUnit, SubscriptionProgress,
  EpisodeTotalSet, CandidateEvaluation pri/trace/unitKeys and decision deferred;
  endpoints subscriptions.search/progress/setEpisodeTotal and subscription-history
- mapping: evaluation messages via describeViolation, pri/trace passthrough

Co-Authored-By: Claude Opus 5.5 <[email protected]>

packages/db/test/schema.test.ts

@@ -90,6 +90,10 @@ const EXPECTED_TABLES = [
   "browser_control_lease",
   // W5-A 文件管理回收站(0024)
   "trash_item",
+  // W5-C 订阅增强(0025)
+  "slot_deferral",
+  "slot_unit",
+  "subscription_history",
 ].sort();
 
 /** 不走 entityTable() 的表:追加型/引擎自有表,没有 uuid id + created_at/updated_at 三件套 */
@@ -257,8 +261,10 @@ describe.skipIf(skip)("schema migrations (real PG)", () => {
       idempotency_key: k,
     });
     await db.insertInto("acquisition_plan").values(plan("k1")).execute();
+    // 0025 起剧集 Slot 允许多个单元不相交的在途计划(服务端在 Slot 行锁内按单元校验);幂等键仍唯一
+    await db.insertInto("acquisition_plan").values(plan("k2")).execute();
     await expect(db.insertInto("acquisition_plan").values(plan("k2")).execute()).rejects.toThrow(
-      /acquisition_plan_slot_active_key/,
+      /acquisition_plan_idempotency_key/,
     );
   });