♻️(backend) replace Django permissions with feature flag decorator

Refactor feature flag mechanism from Django permission classes to custom
decorator that returns 404 Not Found when features are disabled instead
of exposing API structure through permission errors.

Improves security by preventing information disclosure about disabled
features and provides more appropriate response semantics. Custom
decorator approach is better suited for feature toggling than Django's
permission system which is designed for authorization.

src/backend/core/api/permissions.py

@@ -1,7 +1,5 @@
 """Permission handlers for the Meet core app."""
 
-from django.conf import settings
-
 from rest_framework import permissions
 
 from ..models import RoleChoices
@@ -101,36 +99,6 @@ class HasPrivilegesOnRoom(IsAuthenticated):
         return obj.is_administrator_or_owner(request.user)
 
 
-class IsRecordingEnabled(permissions.BasePermission):
-    """Check if the recording feature is enabled."""
-
-    message = "Access denied, recording is disabled."
-
-    def has_permission(self, request, view):
-        """Determine if access is allowed based on settings."""
-        return settings.RECORDING_ENABLE
-
-
-class IsStorageEventEnabled(permissions.BasePermission):
-    """Check if the storage event feature is enabled."""
-
-    message = "Access denied, storage event is disabled."
-
-    def has_permission(self, request, view):
-        """Determine if access is allowed based on settings."""
-        return settings.RECORDING_STORAGE_EVENT_ENABLE
-
-
-class IsSubtitleEnabled(permissions.BasePermission):
-    """Check if the subtitle feature is enabled."""
-
-    message = "Access denied, subtitles are disabled."
-
-    def has_permission(self, request, view):
-        """Determine if access is allowed based on settings."""
-        return settings.ROOM_SUBTITLE_ENABLED
-
-
 class HasLiveKitRoomAccess(permissions.BasePermission):
     """Check if authenticated user's LiveKit token is for the specific room."""