feat(notes): accept and return description field through service and routes

create_note service accepts a new description kwarg and forwards it to the
Note constructor. PUT/PATCH/POST routes include description in the field
whitelist. update_note already passed **fields through setattr, so the new
column is reachable without touching that signature.

src/fabledassistant/services/notes.py

@@ -76,6 +76,7 @@ async def create_note(
     user_id: int,
     title: str = "",
     body: str = "",
+    description: str | None = None,
     tags: list[str] | None = None,
     parent_id: int | None = None,
     project_id: int | None = None,
@@ -103,6 +104,7 @@ async def create_note(
             user_id=user_id,
             title=title,
             body=body,
+            description=description,
             tags=_normalize_tags(tags or []),
             parent_id=parent_id,
             project_id=project_id,