✨(backend) add email invitation endpoint for meeting participants

Implement new endpoint allowing admin/owner to invite participants via email.
Provides explicit way to search users and send meeting invitations with
direct links.

In upcoming commits, frontend will call ResourceAccess endpoint to add
invited people as members if they exist in visio, bypassing waiting room
for a smoother experience.

src/backend/core/api/serializers.py

@@ -223,3 +223,17 @@ class CreationCallbackSerializer(serializers.Serializer):
     def update(self, instance, validated_data):
         """Not implemented as this is a validation-only serializer."""
         raise NotImplementedError("CreationCallbackSerializer is validation-only")
+
+
+class RoomInviteSerializer(serializers.Serializer):
+    """Validate room invite creation data."""
+
+    emails = serializers.ListField(child=serializers.EmailField(), allow_empty=False)
+
+    def create(self, validated_data):
+        """Not implemented as this is a validation-only serializer."""
+        raise NotImplementedError("RoomInviteSerializer is validation-only")
+
+    def update(self, instance, validated_data):
+        """Not implemented as this is a validation-only serializer."""
+        raise NotImplementedError("RoomInviteSerializer is validation-only")

src/backend/core/api/viewsets.py

@@ -41,6 +41,7 @@ from core.recording.worker.factories import (
 from core.recording.worker.mediator import (
     WorkerServiceMediator,
 )
+from core.services.invitation import InvitationService
 from core.services.livekit_events import (
     LiveKitEventsService,
     LiveKitWebhookError,
@@ -497,6 +498,38 @@ class RoomViewSet(
             {"status": "success", "room": room}, status=drf_status.HTTP_200_OK
         )
 
+    @decorators.action(
+        detail=True,
+        methods=["post"],
+        url_path="invite",
+        permission_classes=[
+            permissions.HasPrivilegesOnRoom,
+        ],
+    )
+    def invite(self, request, pk=None):  # pylint: disable=unused-argument
+        """Send email invitations to join a room.
+
+        This API endpoint allows a user with appropriate privileges to send email invitations
+        to one or more recipients, inviting them to join the specified room.
+        """
+
+        room = self.get_object()
+
+        serializer = serializers.RoomInviteSerializer(data=request.data)
+        serializer.is_valid(raise_exception=True)
+
+        emails = serializer.validated_data.get("emails")
+        emails = list(set(emails))
+
+        InvitationService().invite_to_room(
+            room=room, sender=request.user, emails=emails
+        )
+
+        return drf_response.Response(
+            {"status": "success", "message": "invitations sent"},
+            status=drf_status.HTTP_200_OK,
+        )
+
 
 class ResourceAccessListModelMixin:
     """List mixin for resource access API."""