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/backend/src/modules/voice/live-speaker.ts

@@ -0,0 +1,83 @@
+/**
+ * Authoritative live-voice store.
+ *
+ * Single source of truth for who is present / speaking in voice. The backend
+ * WebSocket server is the one relay every frontend client connects to, so it
+ * is the correct place to aggregate the gateway's `voice_active_user` deltas
+ * into a shared snapshot. A late-joining browser must be able to see the same
+ * state as everyone else — this store makes that possible (seeded into the WS
+ * initial states and served via GET /api/voice/status).
+ */
+
+export interface LiveSpeaker {
+  userId: string;
+  username: string;
+  avatar?: string | null;
+  speaking: boolean;
+  /** Epoch ms of the most recent activity (start OR end of speech). */
+  lastActiveAt: number;
+}
+
+const speakers = new Map<string, LiveSpeaker>();
+
+const MAX_SPEAKERS = 200;
+
+/**
+ * Record a voice_active_user event. `speaking: true` upserts the speaker as
+ * active; `speaking: false` marks them inactive while keeping them for the
+ * activity timeline.
+ */
+/**
+ * recordSpeaker(data) — apply a `voice_active_user` event. `speaking: true`
+ * upserts the speaker as ACTIVE; `speaking: false` marks them inactive while
+ * keeping them for the activity timeline.
+ */
+export function recordSpeaker(data: {
+  userId: string;
+  username?: string;
+  avatar?: string | null;
+  speaking: boolean;
+}): void {
+  const { userId, speaking } = data;
+  const existing = speakers.get(userId);
+  const speaker: LiveSpeaker = {
+    userId,
+    username: data.username ?? existing?.username ?? "Unknown",
+    avatar: data.avatar ?? existing?.avatar ?? null,
+    speaking,
+    lastActiveAt: Date.now(),
+  };
+
+  if (speakers.size >= MAX_SPEAKERS && !existing) {
+    // Drop the least-recently-active non-speaking speaker to stay bounded.
+    let oldestId: string | null = null;
+    let oldestTs = Infinity;
+    for (const [id, s] of speakers) {
+      if (!s.speaking && s.lastActiveAt < oldestTs) {
+        oldestTs = s.lastActiveAt;
+        oldestId = id;
+      }
+    }
+    if (oldestId) speakers.delete(oldestId);
+    else return;
+  }
+
+  speakers.set(userId, speaker);
+}
+
+/** All known speakers, most recently active first. */
+export function getActiveSpeakers(): LiveSpeaker[] {
+  return [...speakers.values()].sort((a, b) => b.lastActiveAt - a.lastActiveAt);
+}
+
+/** Only speakers currently flagged as speaking. */
+export function getSpeakingSpeakers(): LiveSpeaker[] {
+  return [...speakers.values()]
+    .filter((s) => s.speaking)
+    .sort((a, b) => b.lastActiveAt - a.lastActiveAt);
+}
+
+/** Drop all tracked speakers (used on backend restart). */
+export function resetLiveSpeakers(): void {
+  speakers.clear();
+}