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.

handlers/support.py

@@ -51,6 +51,7 @@ async def received_message(
     F.message_thread_id.is_not(None),
     F.from_user.is_bot == False,  # noqa: E712
     ~Command("close"),
+    ~Command("refpay"),
     F.text,
 )
 async def handle_admin_message(