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/training.py

@@ -1,6 +1,5 @@
 from fastapi import APIRouter, Depends
 from sqlalchemy.ext.asyncio import AsyncSession
-from typing import Annotated
 from app.database import get_db
 from app.services.corpus_trainer import CorpusTrainer
 from app.api.v1.deps import get_current_user_id
@@ -10,7 +9,7 @@ router = APIRouter()
 
 @router.post("/corpus/run")
 async def run_corpus_training(
-    db: Annotated[AsyncSession, Depends(get_db)] = None,
+    db: AsyncSession = Depends(get_db),
 ):
     trainer = CorpusTrainer(db)
     result = await trainer.run_pipeline()
@@ -20,7 +19,7 @@ async def run_corpus_training(
 @router.post("/corpus/embeddings")
 async def compute_embeddings(
     batch_size: int = 50,
-    db: Annotated[AsyncSession, Depends(get_db)] = None,
+    db: AsyncSession = Depends(get_db),
 ):
     trainer = CorpusTrainer(db)
     result = await trainer.compute_embeddings(batch_size)
@@ -29,7 +28,7 @@ async def compute_embeddings(
 
 @router.get("/corpus/stats")
 async def corpus_stats(
-    db: Annotated[AsyncSession, Depends(get_db)] = None,
+    db: AsyncSession = Depends(get_db),
 ):
     trainer = CorpusTrainer(db)
     return await trainer.get_stats()
@@ -37,7 +36,7 @@ async def corpus_stats(
 
 @router.post("/corpus/deduplicate")
 async def deduplicate_corpus(
-    db: Annotated[AsyncSession, Depends(get_db)] = None,
+    db: AsyncSession = Depends(get_db),
 ):
     trainer = CorpusTrainer(db)
     result = await trainer.deduplicate()