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/shared/ui/tabs.tsx

@@ -0,0 +1,35 @@
+import * as TabsPrimitive from "@radix-ui/react-tabs";
+import type * as React from "react";
+import { cn } from "../lib/utils";
+
+export const Tabs = TabsPrimitive.Root;
+
+export function TabsList({ className, ...props }: React.ComponentPropsWithoutRef<typeof TabsPrimitive.List>) {
+  return (
+    <TabsPrimitive.List
+      className={cn("inline-flex h-10 items-center justify-center rounded-lg bg-muted p-1 text-muted-foreground", className)}
+      {...props}
+    />
+  );
+}
+
+export function TabsTrigger({ className, ...props }: React.ComponentPropsWithoutRef<typeof TabsPrimitive.Trigger>) {
+  return (
+    <TabsPrimitive.Trigger
+      className={cn(
+        "inline-flex items-center justify-center whitespace-nowrap rounded-md px-3 py-1.5 text-sm font-medium transition-all focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring disabled:pointer-events-none disabled:opacity-50 data-[state=active]:bg-background data-[state=active]:text-foreground data-[state=active]:shadow-sm",
+        className,
+      )}
+      {...props}
+    />
+  );
+}
+
+export function TabsContent({ className, ...props }: React.ComponentPropsWithoutRef<typeof TabsPrimitive.Content>) {
+  return (
+    <TabsPrimitive.Content
+      className={cn("mt-6 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring", className)}
+      {...props}
+    />
+  );
+}