refactor(frontend): major rebuild — feature-sliced architecture + bug fixes + glass-morphism UI

Architecture:
- Feature-sliced directory: entities/, shared/, features/, widgets/
- Consolidated API client (shared/api/client.ts) — all endpoints in one file
- Single WebSocket manager (shared/ws/socket.ts) with typed event bus
- Extracted hooks: useAudioPlayback, useAudioTransmit, useLocalStorage, useUIState
- UI primitives moved to shared/ui/ with barrel export
- Added Skeleton, Toast, MobileTabBar components

Bug fixes (8/8):
1. useMemo→useEffect in RecordingsSubPanel (async side-effect anti-pattern)
2. ArrayBuffer.slice() before WebSocket send (shared buffer bug)
3. Proper useEffect dependency arrays throughout
4. Stable React keys (no index fallbacks)
5. onReanalyze properly awaited (Promise<void> return)
6. monitorGuild memoized with useMemo
7. localStorage validation with shape checking
8. Deleted duplicate socket logic (ws/client.ts removed)

UI polish:
- Glass-morphism design tokens (backdrop-blur, translucent cards)
- Gradient mesh background with subtle radial overlays
- Expandable sidebar + mobile bottom tab bar
- Skeleton loading placeholders
- Audio visualizer with CSS pulse animation

Deleted: src/api/, src/components/, src/hooks/, src/types/, src/ws/, src/lib/
Added: 40 new files across feature-sliced structure

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/features/live/components/ActiveSpeakers.tsx

@@ -0,0 +1,46 @@
+import type { ActiveSpeaker } from "../../../shared/api/client";
+import { Skeleton } from "../../../shared/ui";
+
+interface ActiveSpeakersProps {
+  speakers: ActiveSpeaker[];
+}
+
+export function ActiveSpeakers({ speakers }: ActiveSpeakersProps) {
+  if (speakers.length === 0) {
+    return <div className="rounded-xl border border-dashed border-border p-6 text-center text-sm text-muted-foreground">No active speakers.</div>;
+  }
+
+  return (
+    <div className="space-y-2">
+      {speakers.map((s) => {
+        // BUG 4 FIX: stable key — no index fallback
+        const key = s.userId ?? s.id ?? `speaker-${s.username}`;
+        return (
+          <div key={key} className="flex items-center gap-3 rounded-xl border border-border bg-background/60 p-3">
+            <img src={s.avatar} alt="" className="h-8 w-8 rounded-full object-cover" />
+            <div className="min-w-0">
+              <div className="truncate text-sm font-medium">{s.username}</div>
+              <div className="text-xs text-emerald-300">Speaking</div>
+            </div>
+          </div>
+        );
+      })}
+    </div>
+  );
+}
+
+export function ActiveSpeakersSkeleton() {
+  return (
+    <div className="space-y-2">
+      {[1, 2, 3].map((i) => (
+        <div key={i} className="flex items-center gap-3 rounded-xl border border-border bg-background/60 p-3">
+          <Skeleton className="h-8 w-8 rounded-full" />
+          <div className="flex-1 space-y-1">
+            <Skeleton className="h-4 w-24" />
+            <Skeleton className="h-3 w-16" />
+          </div>
+        </div>
+      ))}
+    </div>
+  );
+}