feat: migrate frontend to Astro SSG with design system

- Replace monolithic React SPA (App.tsx) with 7 Astro pages (+ routing)
- Implement full design system from design/ (OKLCH tokens, Tailwind 4 @theme)
- Add 12 Astro components (Button, Badge, Card, Sidebar, Header, states)
- Add 11 React islands (AuthGuard, MessageFeed, VoiceControls, AudioVisualizer, etc.)
- Add 3 Zustand stores (UI, voice, message state)
- Add CSS architecture: dark/light themes, glassmorphism, fluid typography, animations
- Add 404, login, settings, recordings pages
- Remove 40+ legacy React SPA files
- Add Particles background and MascotChat deferred islands
- Wire WebSocket bridge for real-time messages and voice events

Build: 7 pages in ~900ms
Typecheck: clean (0 errors)
Lint: clean (0 errors)

services/frontend/src/shared/ui/card.tsx

@@ -1,67 +0,0 @@
-import type * as React from "react";
-import { cn } from "../lib/utils";
-
-export function Card({
-  className,
-  ...props
-}: React.HTMLAttributes<HTMLDivElement>) {
-  return (
-    <div
-      role="region"
-      className={cn(
-        "rounded-xl border border-border bg-card text-card-foreground shadow-sm hover:shadow-md transition-shadow",
-        className,
-      )}
-      {...props}
-    />
-  );
-}
-
-export function CardHeader({
-  className,
-  ...props
-}: React.HTMLAttributes<HTMLDivElement>) {
-  return (
-    <div
-      className={cn("flex flex-col space-y-1.5 p-6", className)}
-      {...props}
-    />
-  );
-}
-
-export function CardTitle({
-  className,
-  ...props
-}: React.HTMLAttributes<HTMLHeadingElement>) {
-  return (
-    <h3
-      className={cn("font-semibold leading-none tracking-tight", className)}
-      {...props}
-    />
-  );
-}
-
-export function CardDescription({
-  className,
-  ...props
-}: React.HTMLAttributes<HTMLParagraphElement>) {
-  return (
-    <p className={cn("text-sm text-muted-foreground", className)} {...props} />
-  );
-}
-
-export function CardContent({
-  className,
-  ...props
-}: React.HTMLAttributes<HTMLDivElement>) {
-  return <div className={cn("p-6 pt-0", className)} {...props} />;
-}
-
-export function CardFooter({
-  className,
-  ...props
-}: React.HTMLAttributes<HTMLDivElement>) {
-  return (
-    <div className={cn("flex items-center p-6 pt-0", className)} {...props} />
-  );
-}