create migration skeleton for public chat sharing

surfsense_backend/alembic/versions/79_add_public_share_to_chat_threads.py

@@ -0,0 +1,27 @@
+"""Add public sharing columns to new_chat_threads
+
+Revision ID: 79
+Revises: 78
+Create Date: 2026-01-23
+
+Adds public_share_token and public_share_enabled columns to enable
+public sharing of chat threads via secure tokenized URLs.
+"""
+
+from collections.abc import Sequence
+
+# revision identifiers, used by Alembic.
+revision: str = "79"
+down_revision: str | None = "78"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    """Add public sharing columns to new_chat_threads."""
+    pass
+
+
+def downgrade() -> None:
+    """Remove public sharing columns from new_chat_threads."""
+    pass