fix: accept PATCH on /api/tasks/:id (MCP update_task compatibility)

The MCP fable_update_task tool calls PATCH /api/tasks/{id} but the route
only declared PUT. Adding PATCH to the same handler fixes the 405.

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

src/fabledassistant/routes/tasks.py

@@ -117,7 +117,7 @@ async def get_task_route(task_id: int):
     return jsonify(data)
 
 
-@tasks_bp.route("/<int:task_id>", methods=["PUT"])
+@tasks_bp.route("/<int:task_id>", methods=["PUT", "PATCH"])
 @login_required
 async def update_task_route(task_id: int):
     uid = get_current_user_id()