feat: silent wechat login, marketing tab optimization, admin page foundation

- Add silent WeChat login for MP/browser environments
- Fix Python 3.6 compatibility (remove typing.Annotated usage)
- Marketing page: tab-based content generation with category support
- Translate page: add auto-detect language default
- Homepage: add TTS playback, announcement ticker, remove redundant quick-actions
- Fix FAB button overlap with custom tabbar on customers/quotation pages
- Make openai/anthropic imports lazy for Python 3.6 compat

backend/app/api/v1/admin.py

@@ -1,6 +1,5 @@
 from fastapi import APIRouter, Depends, HTTPException, Query
 from sqlalchemy.ext.asyncio import AsyncSession
-from typing import Annotated
 from app.database import get_db
 from app.services.admin import AdminService
 from app.api.v1.deps import get_current_user
@@ -17,7 +16,7 @@ async def require_admin(current_user: dict = Depends(get_current_user)) -> dict:
 @router.get("/dashboard")
 async def get_dashboard(
     _: dict = Depends(require_admin),
-    db: Annotated[AsyncSession, Depends(get_db)] = None,
+    db: AsyncSession = Depends(get_db),
 ):
     service = AdminService(db)
     return await service.get_dashboard()
@@ -28,7 +27,7 @@ async def list_users(
     page: int = Query(1, ge=1),
     size: int = Query(20, ge=1, le=100),
     _: dict = Depends(require_admin),
-    db: Annotated[AsyncSession, Depends(get_db)] = None,
+    db: AsyncSession = Depends(get_db),
 ):
     service = AdminService(db)
     return await service.list_users(page, size)
@@ -39,7 +38,7 @@ async def update_user_tier(
     target_user_id: str,
     data: dict,
     _: dict = Depends(require_admin),
-    db: Annotated[AsyncSession, Depends(get_db)] = None,
+    db: AsyncSession = Depends(get_db),
 ):
     service = AdminService(db)
     tier = data.get("tier")
@@ -55,7 +54,7 @@ async def update_user_tier(
 async def toggle_user_active(
     target_user_id: str,
     _: dict = Depends(require_admin),
-    db: Annotated[AsyncSession, Depends(get_db)] = None,
+    db: AsyncSession = Depends(get_db),
 ):
     service = AdminService(db)
     success = await service.toggle_user_active(target_user_id)
@@ -66,7 +65,7 @@ async def toggle_user_active(
 
 @router.get("/health")
 async def system_health(
-    db: Annotated[AsyncSession, Depends(get_db)] = None,
+    db: AsyncSession = Depends(get_db),
 ):
     service = AdminService(db)
     return await service.get_system_health()