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/button.tsx

@@ -0,0 +1,48 @@
+import { Slot } from "@radix-ui/react-slot";
+import type * as React from "react";
+import { cn } from "../lib/utils";
+
+type ButtonVariant = "default" | "secondary" | "destructive" | "outline" | "ghost";
+type ButtonSize = "default" | "sm" | "lg" | "icon";
+
+const variants: Record<ButtonVariant, string> = {
+  default: "bg-primary text-primary-foreground shadow hover:bg-primary/90",
+  secondary: "bg-secondary text-secondary-foreground hover:bg-secondary/80",
+  destructive: "bg-destructive text-destructive-foreground hover:bg-destructive/90",
+  outline: "border border-border bg-background hover:bg-accent hover:text-accent-foreground",
+  ghost: "hover:bg-accent hover:text-accent-foreground",
+};
+
+const sizes: Record<ButtonSize, string> = {
+  default: "h-10 px-4 py-2",
+  sm: "h-9 rounded-md px-3",
+  lg: "h-11 rounded-md px-8",
+  icon: "h-10 w-10",
+};
+
+export interface ButtonProps extends React.ButtonHTMLAttributes<HTMLButtonElement> {
+  asChild?: boolean;
+  variant?: ButtonVariant;
+  size?: ButtonSize;
+}
+
+export function Button({
+  className,
+  variant = "default",
+  size = "default",
+  asChild = false,
+  ...props
+}: ButtonProps) {
+  const Comp = asChild ? Slot : "button";
+  return (
+    <Comp
+      className={cn(
+        "inline-flex items-center justify-center gap-2 whitespace-nowrap rounded-lg text-sm font-medium transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring disabled:pointer-events-none disabled:opacity-50",
+        variants[variant],
+        sizes[size],
+        className,
+      )}
+      {...props}
+    />
+  );
+}