Add referral system and user balance tracking

Introduce balance field to User model with Alembic migration. Add
referral menu, admin /refpay command, and deep link sharing. Update
Dockerfile to multi-stage build and add Postgres service to compose.
Fix deep link parsing logic and conditional proxy initialization.

main.py

@@ -38,7 +38,7 @@ async def main():
     )
     dp.update.middleware.register(DIMiddleware(deps, async_session))
 
-    aiohttp_session = AiohttpSession(proxy=settings.proxy)
+    aiohttp_session = AiohttpSession(proxy=settings.proxy) if settings.proxy else None
     default = DefaultBotProperties(parse_mode="HTML")
     bot = Bot(token=settings.bot_token, default=default, session=aiohttp_session)