📈(frontend) track missing lobby participant on accept/reject

When a moderator accepts or rejects a lobby entry that no longer
exists, emit a tracking event so we can measure how often it
happens.

This signal will help tune the lobby polling interval: too many
"not found" events means the moderator side is working from a stale
list. Keep raising the error to the client on top of tracking it,
so the frontend still surfaces the issue (its current handling of
this case is still incomplete).

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to
 - ✨(backend) add Traefik support via configurable media-auth url header #1649
 - ✨(backend) update a room's attributes from the external API
 - 🔊(backend) log request duration in Gunicorn workers
+- 📈(frontend) track missing lobby participant on accept/reject
 
 ### Changed
 

src/frontend/src/features/participants/api/enterRoom.ts

@@ -1,5 +1,6 @@
 import { ApiError } from '@/api/ApiError'
 import { fetchApi } from '@/api/fetchApi'
+import { captureEvent } from '@/features/analytics/telemetry'
 import { useMutation, type UseMutationOptions } from '@tanstack/react-query'
 
 export interface EnterRoomParams {
@@ -17,13 +18,23 @@ export const enterRoom = async ({
   allowEntry,
   participantId,
 }: EnterRoomParams): Promise<EnterRoomResponse> => {
-  return await fetchApi<EnterRoomResponse>(`/rooms/${roomId}/enter/`, {
-    method: 'POST',
-    body: JSON.stringify({
-      participant_id: participantId,
-      allow_entry: allowEntry,
-    }),
-  })
+  try {
+    return await fetchApi<EnterRoomResponse>(`/rooms/${roomId}/enter/`, {
+      method: 'POST',
+      body: JSON.stringify({
+        participant_id: participantId,
+        allow_entry: allowEntry,
+      }),
+    })
+  } catch (error) {
+    if (error instanceof ApiError && error.statusCode === 404) {
+      captureEvent('lobby_entry_participant_gone', {
+        room_id: roomId,
+        allow_entry: allowEntry,
+      })
+    }
+    throw error
+  }
 }
 
 export function useEnterRoom(