feat(privacy): add private-message permission toggle

alembic/versions/0012_user_private_message_privacy.py

@@ -0,0 +1,28 @@
+"""add allow_private_messages setting
+
+Revision ID: 0012_user_private_message_privacy
+Revises: 0011_chat_public_id
+Create Date: 2026-03-08 16:00:00.000000
+"""
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision: str = "0012_user_private_message_privacy"
+down_revision: Union[str, Sequence[str], None] = "0011_chat_public_id"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "users",
+        sa.Column("allow_private_messages", sa.Boolean(), nullable=False, server_default=sa.text("true")),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("users", "allow_private_messages")