fix: migrate all remaining naive timestamp columns to timestamptz

Old universal_migration.py created some tables (including email_templates)
with `timestamp` (naive) columns and had a catch-all that converted all
naive columns to `timestamptz` on each startup. After switching to Alembic,
that catch-all stopped running.

Users whose email_templates table was created by universal_migration.py
before the catch-all ran still have naive `timestamp` columns. The code
uses `datetime.now(UTC)` (timezone-aware), causing asyncpg to raise:
  "can't subtract offset-naive and offset-aware datetimes"

Migration 0007 finds and converts ALL remaining naive timestamp columns
in public schema to timestamptz, assuming UTC for existing data.

Fixes: email template save returning 503 with DataError

migrations/alembic/versions/0007_fix_naive_timestamps.py

@@ -0,0 +1,67 @@
+"""fix all remaining naive timestamp columns to timestamptz
+
+Revision ID: 0007
+Revises: 0006
+Create Date: 2026-02-23
+
+The old universal_migration.py created some tables with `timestamp` (naive)
+columns and had a catch-all migration that converted ALL naive timestamp
+columns to `timestamptz` on every startup. When universal_migration.py was
+replaced with Alembic, that catch-all migration stopped running.
+
+Databases where `email_templates` (and potentially other tables) were created
+by universal_migration.py before the catch-all ran still have naive columns.
+The code uses `datetime.now(UTC)` (timezone-aware), causing asyncpg to raise:
+  "can't subtract offset-naive and offset-aware datetimes"
+
+This migration finds and converts ALL remaining naive timestamp columns
+in public schema to timestamptz, assuming UTC for existing data.
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = '0007'
+down_revision: Union[str, None] = '0006'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    conn = op.get_bind()
+
+    # Find all naive timestamp columns in public schema
+    result = conn.execute(
+        sa.text("""
+            SELECT table_name, column_name
+            FROM information_schema.columns
+            WHERE table_schema = 'public'
+              AND data_type = 'timestamp without time zone'
+            ORDER BY table_name, column_name
+        """)
+    )
+    columns = result.fetchall()
+
+    if not columns:
+        return
+
+    # Set timezone context for the conversion
+    conn.execute(sa.text("SET LOCAL timezone = 'UTC'"))
+
+    for table_name, column_name in columns:
+        op.execute(
+            sa.text(
+                f'ALTER TABLE "{table_name}" '
+                f'ALTER COLUMN "{column_name}" TYPE TIMESTAMPTZ '
+                f"USING \"{column_name}\" AT TIME ZONE 'UTC'"
+            )
+        )
+
+
+def downgrade() -> None:
+    # No-op: converting back to naive timestamps would lose timezone info
+    # and re-introduce the original bug.
+    pass