♻️(backend) control metadata collector agent launch via feature flag

Allow controlling when the metadata collector agent is started,
enabling users to try the feature and disable it if needed.

Introduce a user-level feature flag to toggle the agent for the
initial release.

src/backend/core/api/serializers.py

@@ -232,11 +232,14 @@ class RecordingOptions(BaseModel):
             When `None`, falls back to the application default.
         original_mode: The original recording mode before any override.
             Must be one of the valid RecordingModeChoices values when provided.
+        collect_metadata: Whether to collect additional metadata during recording.
+            When `None`, no metadata are collected.
 
     """
 
     language: str | None = None
     transcribe: bool | None = None
+    collect_metadata: bool | None = None
     original_mode: Literal["screen_recording", "transcript"] | None = None
 
     model_config = {"extra": "forbid"}

src/backend/core/api/viewsets.py

@@ -343,8 +343,7 @@ class RoomViewSet(
             )
 
         if settings.METADATA_COLLECTOR_ENABLED and (
-            recording.mode == models.RecordingModeChoices.TRANSCRIPT
-            or recording.options.get("transcribe", False)
+            recording.options.get("collect_metadata", False)
         ):
             try:
                 MetadataCollectorService().start(recording)