Add basic FastAPI auth and React login gate

frontend/src/pages/LoginPage.tsx

@@ -0,0 +1,19 @@
+import { useState } from 'react';
+
+type Props = { onLogin: (token: string) => void };
+export function LoginPage({ onLogin }: Props) {
+  const [username, setUsername] = useState('admin');
+  const [password, setPassword] = useState('admin123');
+  const [error, setError] = useState('');
+  const [loading, setLoading] = useState(false);
+  const submit = async (e: React.FormEvent) => {
+    e.preventDefault(); setLoading(true); setError('');
+    try {
+      const body = new URLSearchParams(); body.set('username', username); body.set('password', password);
+      const res = await fetch('/auth/token', { method: 'POST', body });
+      if (!res.ok) throw new Error('Login fallito');
+      const data = await res.json(); onLogin(data.access_token);
+    } catch (err) { setError(err instanceof Error ? err.message : 'Login fallito'); } finally { setLoading(false); }
+  };
+  return <main className="login-page"><section className="login-card"><p className="login-eyebrow">NetMapper auth</p><h1>Accedi al book of truth</h1><p className="login-copy">L'accesso è protetto per impedire lettura e modifica dei dati da terzi.</p><form onSubmit={submit} className="login-form"><label>Username<input value={username} onChange={(e) => setUsername(e.target.value)} /></label><label>Password<input type="password" value={password} onChange={(e) => setPassword(e.target.value)} /></label>{error && <p className="login-error">{error}</p>}<button type="submit" disabled={loading}>{loading ? 'Accesso...' : 'Entra'}</button></form></section></main>;
+}