fix: register m0004 add_mentor_note migration

Co-authored-by: multica-agent <github@multica.ai>

app/backend/database/migrations/m0004_mentor_notes.py

@@ -0,0 +1,24 @@
+from __future__ import annotations
+
+import sqlite3
+
+from backend.database.migrations.runner import Migration
+
+
+def add_mentor_note(connection: sqlite3.Connection) -> None:
+    columns = {
+        str(row["name"])
+        for row in connection.execute("PRAGMA table_info(mentor_preferences)")
+    }
+    if "note" not in columns:
+        connection.execute(
+            "ALTER TABLE mentor_preferences ADD COLUMN note TEXT NOT NULL DEFAULT ''"
+        )
+
+
+MIGRATION = Migration(
+    version="0004",
+    name="add_mentor_note",
+    action=add_mentor_note,
+    signature="mentor-preferences-note:v1:note",
+)