feat(ad): eCPM 上报接口 + 冷却策略解耦纯函数 + savings JSONB 跨库修复 (#8)

- 新增 POST /api/v1/ad/ecpm-report:激励视频展示后客户端上报本次 eCPM,落 ad_ecpm_record 做内部收益统计(model/repository/schema/alembic 迁移 + 接口文档)
- 看广告冷却策略抽到 app/core/ad_cooldown.py 纯函数;ad_reward.today_status 只取数据,换策略只改这一处
- savings.dishes 改 JSON().with_variant(JSONB,"postgresql"):SQLite 无 visit_JSONB 会让 create_all 编译崩,修复后测试套件恢复

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: OuYingJun1024 <1034284404@qq.com>
Reviewed-on: #8
Co-authored-by: ouzhou <ouzhou@wonderable.ai>
Co-committed-by: ouzhou <ouzhou@wonderable.ai>

app/models/__init__.py

@@ -1,5 +1,8 @@
 """所有 ORM model 必须在这里 import 一次,Alembic / metadata 才能扫到。"""
+from app.models.ad_ecpm import AdEcpmRecord  # noqa: F401
 from app.models.ad_reward import AdRewardRecord  # noqa: F401
+from app.models.comparison import ComparisonRecord  # noqa: F401
+from app.models.comparison_milestone import ComparisonMilestoneClaim  # noqa: F401
 from app.models.feedback import Feedback  # noqa: F401
 from app.models.savings import SavingsRecord  # noqa: F401
 from app.models.signin import SigninRecord  # noqa: F401