feat(ad): 穿山甲广告配置后台化(app_id/各位ID/验签密钥/各场景开关)

- app_config 存 ad_config(默认=客户端当前内置 ID,空库维持现状)
- GET /platform/ad-config 下发客户端(不含验签密钥 reward_mkey)
- admin GET/PATCH /admin/api/ad-config 读写(operator/finance + 审计,mkey 不记明文)
- pangle 回调验签 m-key 优先读后台配置、.env 兜底兼容
- 比价/领券信息流位拆分(compare/coupon_feed_code_id)
- 客户端需发版接入 /platform/ad-config 才生效;本次后端就绪、不影响现状

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

app/admin/main.py

@@ -14,6 +14,7 @@ from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
 from app.admin.routers.ad_audit import router as ad_audit_router
+from app.admin.routers.ad_config import router as ad_config_router
 from app.admin.routers.ad_revenue import router as ad_revenue_router
 from app.admin.routers.admins import router as admins_router
 from app.admin.routers.audit import router as audit_router
@@ -95,4 +96,5 @@ admin_app.include_router(config_router)
 admin_app.include_router(comparison_router)
 admin_app.include_router(cps_router)
 admin_app.include_router(ad_audit_router)
+admin_app.include_router(ad_config_router)
 admin_app.include_router(ad_revenue_router)