feat(platform): 首页门面三统计 + 运营后台展示模式配置

- 新表 platform_stat_display:每个指标可选 real/manual/random 三种
  展示模式,含建表 + anchor_minutes 两个 alembic migration
- 公开接口 GET /api/v1/platform/stats(无鉴权门面数字,登录前可读)
- 运营后台 GET/PATCH /admin/api/dashboard-display 配置展示模式
- 配套 model/repository/schema,注册 router(app/main+admin/main),
  导出 model,补 docs(api/database 索引及 3 篇详情)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/admin/main.py

@@ -18,6 +18,7 @@ from app.admin.routers.audit import router as audit_router
 from app.admin.routers.auth import router as auth_router
 from app.admin.routers.config import router as config_router
 from app.admin.routers.dashboard import router as dashboard_router
+from app.admin.routers.dashboard_display import router as dashboard_display_router
 from app.admin.routers.feedback import router as feedback_router
 from app.admin.routers.users import router as users_router
 from app.admin.routers.wallet import router as wallet_router
@@ -73,6 +74,7 @@ def health() -> dict[str, str]:
 
 admin_app.include_router(auth_router)
 admin_app.include_router(dashboard_router)
+admin_app.include_router(dashboard_display_router)
 admin_app.include_router(users_router)
 admin_app.include_router(wallet_router)
 admin_app.include_router(withdraw_router)