Add register + logout auth flows, and batch-5 resources

Auth (hand-built, uses the auth core):
- /register + register() action: validates, hashes with argon2id (hashPassword),
  creates an emulator-compatible users row (accountCreated/ipRegister/ipCurrent/
  look), redirect kept outside try so NEXT_REDIRECT propagates. Login/register
  cross-links; header shows Register (logged-out) and a Logout (signOut) button.

Batch 5 (parallel agents): /admin/rooms (+[id]) search+detail, /admin/vouchers
(CRUD), /admin/subscriptions (read), /admin/calendar (campaigns+rewards read),
/marketplace (public). Header + admin nav extended.

Verified: tsc exit 0, vitest 48/48, next build exit 0 (52 page routes).

src/app/register/page.tsx

@@ -0,0 +1,43 @@
+import Link from "next/link";
+import { register } from "@/actions/register";
+
+export default async function RegisterPage({
+  searchParams,
+}: {
+  searchParams: Promise<{ error?: string }>;
+}) {
+  const { error } = await searchParams;
+
+  return (
+    <main style={{ maxWidth: 400, margin: "2rem auto" }}>
+      <div className="card" style={{ padding: "1.75rem" }}>
+        <h1 style={{ marginTop: 0, textAlign: "center" }}>Create account</h1>
+        <p className="muted" style={{ textAlign: "center", marginTop: 0 }}>
+          Join the hotel — it only takes a moment.
+        </p>
+        <form action={register} style={{ display: "grid", gap: "0.7rem", marginTop: "1rem" }}>
+          <input name="username" placeholder="Username" autoComplete="username" required />
+          <input name="mail" type="email" placeholder="Email" autoComplete="email" required />
+          <input
+            name="password"
+            type="password"
+            placeholder="Password (min 6 chars)"
+            autoComplete="new-password"
+            required
+          />
+          <button type="submit" className="btn btn-primary">
+            Register
+          </button>
+        </form>
+        {error ? (
+          <p style={{ color: "var(--color-danger)", textAlign: "center", marginBottom: 0 }}>
+            {error}
+          </p>
+        ) : null}
+        <p className="muted" style={{ textAlign: "center", marginBottom: 0, marginTop: "1rem" }}>
+          Already have an account? <Link href="/login">Sign in</Link>
+        </p>
+      </div>
+    </main>
+  );
+}