refactor(fe): align dashboard with backend & gateway data flow

- API/WS clients: same-origin by default, drop dead imphnen hardcode
- chatbot history: map BE rows {user_message,bot_response,created_at}
- message_deleted WS payload: object {id,deleted_at}, not bare string
- dashboard: wire top-channels chart + live mod queue from /api/review,
  add Users & Channels tabs consuming /api/dashboard/users|channels
- recordings: live WS sync via voice_recording_uploaded; duration_bytes optional
- remove dead widgets with no BE data source (trend chart, heatmap)

services/frontend/src/hooks/use-dashboard.ts

@@ -22,12 +22,11 @@ export function useUsers(search?: string) {
   });
 }
 
-export function useChannels(guildId: string, search?: string) {
+export function useChannels(guildId?: string, search?: string) {
   return useQuery({
-    queryKey: ["dashboard-channels", guildId, search ?? ""],
+    queryKey: ["dashboard-channels", guildId ?? "__all__", search ?? ""],
     queryFn: () => dashboardApi.listChannels(20, search, guildId || undefined),
     select: (data) => data.data,
-    enabled: !!guildId,
   });
 }