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/widgets/DashboardLayout.tsx

@@ -0,0 +1,28 @@
+import type { ReactNode } from "react";
+import type { DashboardTab } from "../entities/ui/types";
+import type { WsStatus } from "../shared/ws/socket";
+import type { VoiceStatus } from "../shared/api/client";
+import { Header } from "./Header";
+import { Sidebar } from "./Sidebar";
+
+interface DashboardLayoutProps {
+  activeTab: DashboardTab;
+  wsStatus: WsStatus;
+  voiceStatus: VoiceStatus;
+  onTabChange: (tab: DashboardTab) => void;
+  children: ReactNode;
+}
+
+export function DashboardLayout({ activeTab, wsStatus, voiceStatus, onTabChange, children }: DashboardLayoutProps) {
+  return (
+    <div className="min-h-screen bg-background text-foreground">
+      <div className="flex min-h-screen">
+        <Sidebar activeTab={activeTab} onTabChange={onTabChange} />
+        <main className="flex min-w-0 flex-1 flex-col">
+          <Header activeTab={activeTab} wsStatus={wsStatus} voiceStatus={voiceStatus} />
+          <div className="flex-1 overflow-auto p-4 md:p-6 lg:p-8">{children}</div>
+        </main>
+      </div>
+    </div>
+  );
+}