API: no_project filter + project_id on tasks route

- list_notes(): add no_project param → Note.project_id.is_(None) filter
- GET /api/notes: expose ?no_project=true
- GET /api/tasks: add ?project_id= and ?no_project=true pass-through

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/fabledassistant/services/notes.py

@@ -85,6 +85,7 @@ async def list_notes(
     milestone_id: int | None = None,
     milestone_ids: list[int] | None = None,
     parent_id: int | None = None,
+    no_project: bool = False,
     sort: str = "updated_at",
     order: str = "desc",
     limit: int = 50,
@@ -152,6 +153,10 @@ async def list_notes(
 
         if parent_id is not None:
             query = query.where(Note.parent_id == parent_id)
+
+        if no_project:
+            query = query.where(Note.project_id.is_(None))
+            count_query = count_query.where(Note.project_id.is_(None))
             count_query = count_query.where(Note.parent_id == parent_id)
 
         sort_col = getattr(Note, sort, Note.updated_at)