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.

alembic/versions/f40cab941564_user_balance.py

@@ -0,0 +1,32 @@
+"""user -> +balance.
+
+Revision ID: f40cab941564
+Revises: 5985b2df0830
+Create Date: 2026-04-10 21:11:15.209314
+
+"""
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision: str = "f40cab941564"
+down_revision: Union[str, Sequence[str], None] = "5985b2df0830"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.add_column("users", sa.Column("balance", sa.INTEGER(), nullable=False))
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_column("users", "balance")
+    # ### end Alembic commands ###