feat: add m365 shared mailbox folder selection

backend/alembic/versions/c4d5e6f7a8b9_add_m365_folder_selection.py

@@ -0,0 +1,25 @@
+"""Add Microsoft 365 folder selection.
+
+Revision ID: c4d5e6f7a8b9
+Revises: f3a4b5c6d7e8
+Create Date: 2026-05-23 00:00:00.000000
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "c4d5e6f7a8b9"
+down_revision: Union[str, Sequence[str], None] = "f3a4b5c6d7e8"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column("mail_sources", sa.Column("m365_folder_id", sa.String(), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column("mail_sources", "m365_folder_id")