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.

db/models/users.py

@@ -1,4 +1,4 @@
-from sqlalchemy import BIGINT, TEXT
+from sqlalchemy import BIGINT, INTEGER, TEXT
 from sqlalchemy.orm import Mapped, mapped_column
 
 from db.base import Base
@@ -12,3 +12,4 @@ class User(Base):
     )
     referal_id: Mapped[int] = mapped_column(BIGINT, nullable=True)
     subscription_link: Mapped[str] = mapped_column(TEXT, nullable=True, unique=True)
+    balance: Mapped[int] = mapped_column(INTEGER, nullable=False, default=0)