feat(frontend): Task 14 - Vite React TypeScript scaffolding with Tailwind CSS

Sets up the frontend SPA foundation: Vite+React+TS project at frontend/,
configures Tailwind CSS v4 via @tailwindcss/vite, dev proxy to port 4000,
and implements the API client (JWT auth, auto-redirect on 401).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

display/frontend/src/api/client.ts

@@ -0,0 +1,48 @@
+const TOKEN_KEY = 'display_token';
+
+export function getToken(): string | null {
+  return localStorage.getItem(TOKEN_KEY);
+}
+
+export function setToken(token: string): void {
+  localStorage.setItem(TOKEN_KEY, token);
+}
+
+export function clearToken(): void {
+  localStorage.removeItem(TOKEN_KEY);
+}
+
+export function isLoggedIn(): boolean {
+  return !!getToken();
+}
+
+async function request<T>(method: string, path: string, body?: unknown): Promise<T> {
+  const headers: Record<string, string> = { 'Content-Type': 'application/json' };
+  const token = getToken();
+  if (token) headers['Authorization'] = `Bearer ${token}`;
+
+  const res = await fetch(path, {
+    method,
+    headers,
+    body: body !== undefined ? JSON.stringify(body) : undefined,
+  });
+
+  if (res.status === 401) {
+    clearToken();
+    window.location.href = '/login';
+    throw new Error('Unauthorized');
+  }
+
+  if (res.status === 204) return undefined as T;
+
+  const data = await res.json();
+  if (!res.ok) throw new Error(data.error ?? `HTTP ${res.status}`);
+  return data as T;
+}
+
+export const api = {
+  get: <T>(path: string) => request<T>('GET', path),
+  post: <T>(path: string, body?: unknown) => request<T>('POST', path, body),
+  put: <T>(path: string, body?: unknown) => request<T>('PUT', path, body),
+  del: <T>(path: string) => request<T>('DELETE', path),
+};

display/frontend/src/index.css

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+@import "tailwindcss";

display/frontend/src/main.tsx

@@ -0,0 +1,10 @@
+import { StrictMode } from 'react';
+import { createRoot } from 'react-dom/client';
+import './index.css';
+import App from './App.tsx';
+
+createRoot(document.getElementById('root')!).render(
+  <StrictMode>
+    <App />
+  </StrictMode>,
+);