feat(frontend): rebuild as SSR with server-authoritative shared state

Rombak total alur data frontend: dari static-export CSR (tiap browser
fetch sendiri + akumulasi state voice per-tab) jadi server-side rendering.

Frontend (Next.js):
- next.config: output export -> standalone; halaman jadi server components
- server data layer baru src/lib/api/server.ts (GMW_BACKEND_URL, no window)
- dashboard/media/messages/moderation/recordings/voice page -> RSC yang
  fetch backend di render-time, seed ke client view (SWR fallbackData)
- hook-hook utama terima initialData -> first paint data server, revalidate
  SWR setelahnya, tanpa spinner-blank-load
- messages: guild/channel/tab/selected dibaca dari URL di server, page awal
  di-fetch server-side

Shared realtime state (voice) server-authoritative:
- backend src/modules/voice/live-speaker.ts: agregat voice_active_user dari
  gateway jadi snapshot authoritatif (single source of truth semua browser)
- GET /api/voice/status kini include activeSpeakers
- WS initial states kirim voice_state snapshot saat connect (late join
  langsung dapat state yang sama, bukan daftar kosong)
- useSpeakers seed dari server snapshot + voice_state full-replace +
  voice_active_user delta upsert

Deploy:
- flake.nix: frontend package build SSR standalone (server.js wrapper,
  GMW_FRONTEND_PORT=4017); proxy nginx template proxy / -> Next server,
  /api + /ws tetap ke backend :4001

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

@@ -10,15 +10,26 @@ import type {
   TopReactor,
 } from "@/lib/types";
 
-export function useStats() {
-  return useSWR<DashboardStats>(["dashboard-stats"], () =>
-    dashboardApi.getStats(),
+/**
+ * Server-seeded SWR hooks.
+ *
+ * SSR pages fetch the initial payload on the server and hand it here as
+ * `initialData` — the first render is server data, and SWR takes over for
+ * revalidation from then on (no blank-spinner-first-load).
+ */
+export function useStats(initialData?: DashboardStats) {
+  return useSWR<DashboardStats>(
+    ["dashboard-stats"],
+    () => dashboardApi.getStats(),
+    { fallbackData: initialData },
   );
 }
 
-export function useActivity(days = 14) {
-  return useSWR<DashboardActivity>(["dashboard-activity", days], () =>
-    dashboardApi.getActivity(days),
+export function useActivity(days = 14, initialData?: DashboardActivity) {
+  return useSWR<DashboardActivity>(
+    ["dashboard-activity", days],
+    () => dashboardApi.getActivity(days),
+    { fallbackData: initialData },
   );
 }