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/payment.py

@@ -1,6 +1,5 @@
 from fastapi import APIRouter, Depends, HTTPException
 from sqlalchemy.ext.asyncio import AsyncSession
-from typing import Annotated
 from pydantic import BaseModel
 from app.database import get_db
 from app.services.payment import PaymentService
@@ -27,7 +26,7 @@ async def get_plans():
 @router.get("/subscription")
 async def get_subscription(
     user_id: str = Depends(get_current_user_id),
-    db: Annotated[AsyncSession, Depends(get_db)] = None,
+    db: AsyncSession = Depends(get_db),
 ):
     svc = PaymentService(db)
     return await svc.get_current_subscription(user_id)
@@ -37,7 +36,7 @@ async def get_subscription(
 async def create_order(
     data: CreateOrderRequest,
     user_id: str = Depends(get_current_user_id),
-    db: Annotated[AsyncSession, Depends(get_db)] = None,
+    db: AsyncSession = Depends(get_db),
 ):
     svc = PaymentService(db)
     try:
@@ -49,7 +48,7 @@ async def create_order(
 @router.post("/callback")
 async def payment_callback(
     data: PaymentCallbackRequest,
-    db: Annotated[AsyncSession, Depends(get_db)] = None,
+    db: AsyncSession = Depends(get_db),
 ):
     svc = PaymentService(db)
     success = await svc.handle_payment_callback(data.payment_id, data.success)