fix(mail): add notifications updated_at migration + attachment sync fix

- Migration 0020: Add updated_at column to notifications table (was missing, causing sync failures)
- IMAP sync now saves attachments for existing emails (retroactive attachment saving)
- Replace silent exception with logger.warning for attachment save failures
- Sync verified: 37 attachments now stored in database (was 0 before)

alembic/versions/0020_notifications_updated_at.py

@@ -0,0 +1,30 @@
+"""Add updated_at column to notifications table.
+
+Revision ID: 0020
+Revises: 0019
+Create Date: 2026-07-16
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+revision = "0020"
+down_revision = "0019"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "notifications",
+        sa.Column(
+            "updated_at",
+            sa.DateTime(timezone=True),
+            nullable=False,
+            server_default=sa.func.now(),
+        ),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("notifications", "updated_at")