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.

repositories/users.py

@@ -47,3 +47,25 @@ class UserRepository:
 
         await session.commit()
         return user
+
+    async def update_user_balance(
+        self, session: AsyncSession, user_id: int, balance: int
+    ) -> Optional[User]:
+        user = await self.get_user_by_id(session, user_id=user_id)
+        if not user:
+            return None
+        user.balance = balance
+
+        await session.commit()
+        return user
+
+    async def increase_user_balance(
+        self, session: AsyncSession, user_id: int, amount: int
+    ) -> Optional[User]:
+        user = await self.get_user_by_id(session, user_id=user_id)
+        if not user:
+            return None
+        user.balance += amount
+
+        await session.commit()
+        return user