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/onboarding.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.onboarding import OnboardingService
@@ -19,7 +18,7 @@ class OnboardingRequest(BaseModel):
 @router.get("/status")
 async def get_status(
     user_id: str = Depends(get_current_user_id),
-    db: Annotated[AsyncSession, Depends(get_db)] = None,
+    db: AsyncSession = Depends(get_db),
 ):
     service = OnboardingService(db)
     return await service.check_status(user_id)
@@ -29,7 +28,7 @@ async def get_status(
 async def create_first_product(
     data: OnboardingRequest,
     user_id: str = Depends(get_current_user_id),
-    db: Annotated[AsyncSession, Depends(get_db)] = None,
+    db: AsyncSession = Depends(get_db),
 ):
     if not data.name.strip():
         raise HTTPException(status_code=400, detail="Product name is required")