feat(core): add alembic migration for soft-delete columns on core tables

alembic/versions/0012_soft_delete.py

@@ -0,0 +1,47 @@
+"""Add deleted_at column to core tables that don't have it yet.
+
+Revision ID: 0012_soft_delete
+Revises: 0011_attachments
+Create Date: 2026-07-04
+"""
+
+from __future__ import annotations
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+revision: str = "0012_soft_delete"
+down_revision: Union[str, None] = "0011_attachments"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+# Core tables that need deleted_at added
+# Excludes: audit_log (immutable), deletion_log (already has it),
+# tenants (top-level), user_tenants (join table with cascade delete)
+TABLES_NEEDING_SOFT_DELETE = [
+    "users",
+    "roles",
+    "sessions",
+    "notifications",
+    "ai_conversations",
+    "ai_messages",
+    "workflows",
+    "workflow_instances",
+    "workflow_step_history",
+    "company_contacts",
+]
+
+
+def upgrade() -> None:
+    for table_name in TABLES_NEEDING_SOFT_DELETE:
+        op.add_column(
+            table_name,
+            sa.Column("deleted_at", sa.DateTime(timezone=True), nullable=True),
+        )
+
+
+def downgrade() -> None:
+    for table_name in reversed(TABLES_NEEDING_SOFT_DELETE):
+        op.drop_column(table_name, "deleted_at")