feat(comments): add reply threading + UI

backend/alembic/versions/9d3d9b9c1a23_add_reply_to_task_comments.py

@@ -0,0 +1,32 @@
+"""add reply_to_comment_id to task_comments
+
+Revision ID: 9d3d9b9c1a23
+Revises: 157587037601
+Create Date: 2026-02-02 08:15:00.000000
+
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision = "9d3d9b9c1a23"
+down_revision = "157587037601"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("task_comments", sa.Column("reply_to_comment_id", sa.Integer(), nullable=True))
+    op.create_foreign_key(
+        "fk_task_comments_reply_to_comment_id",
+        "task_comments",
+        "task_comments",
+        ["reply_to_comment_id"],
+        ["id"],
+    )
+
+
+def downgrade() -> None:
+    op.drop_constraint("fk_task_comments_reply_to_comment_id", "task_comments", type_="foreignkey")
+    op.drop_column("task_comments", "reply_to_comment_id")