Add Redis caching, email refresh button, optimize page loading

- Add Redis service (docker-compose) for caching accounts, messages, payment status
- Cache accounts list (5min), messages (3min), payment status (10min)
- Auto-invalidate cache on import/delete/payment-check/note-update
- Add refresh button to email list panel (force re-fetch from IMAP)
- Messages API supports refresh=true param to bypass cache
- New cache.py module with RedisCache class

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

requirements.txt

@@ -4,4 +4,5 @@ pydantic[email]==2.5.0
 httpx==0.25.2
 python-multipart==0.0.6
 jinja2==3.1.2
-aiofiles==23.2.1
+aiofiles==23.2.1
+redis[hiredis]==5.0.1