feat(admin): bearer auth with admin-only gate + login screen

apps/admin/src/screens/Login.tsx

@@ -0,0 +1,57 @@
+import { useState, type FormEvent } from 'react';
+import { NotAdminError, useAuth } from '../auth/AuthContext';
+
+export default function Login() {
+  const { signIn } = useAuth();
+  const [email, setEmail] = useState('');
+  const [password, setPassword] = useState('');
+  const [error, setError] = useState<string | null>(null);
+  const [busy, setBusy] = useState(false);
+
+  async function handleSubmit(e: FormEvent) {
+    e.preventDefault();
+    setError(null);
+    setBusy(true);
+    try {
+      await signIn(email, password);
+    } catch (err) {
+      setError(
+        err instanceof NotAdminError ? 'Geen toegang — alleen beheerders.' : 'Inloggen mislukt'
+      );
+    } finally {
+      setBusy(false);
+    }
+  }
+
+  return (
+    <div className="login">
+      <h1 className="login-title">SoleLog Admin</h1>
+      <form className="login-form" onSubmit={handleSubmit}>
+        <label className="field">
+          <span className="field-label">E-mailadres</span>
+          <input
+            className="field-input"
+            type="email"
+            autoComplete="email"
+            value={email}
+            onChange={(e) => setEmail(e.target.value)}
+          />
+        </label>
+        <label className="field">
+          <span className="field-label">Wachtwoord</span>
+          <input
+            className="field-input"
+            type="password"
+            autoComplete="current-password"
+            value={password}
+            onChange={(e) => setPassword(e.target.value)}
+          />
+        </label>
+        {error && <p className="login-error">{error}</p>}
+        <button className="btn-primary" type="submit" disabled={busy}>
+          Inloggen
+        </button>
+      </form>
+    </div>
+  );
+}