feat(auth): preserve redirect URL when redirecting to /login

Appends ?redirect= with the original pathname so the login page
can redirect back after successful authentication.

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

frontend/src/hooks.server.ts

@@ -13,6 +13,11 @@ function isPublicRoute(pathname: string): boolean {
 	return PUBLIC_ROUTES.some((route) => pathname === route || pathname.startsWith(route + '/'));
 }
 
+function loginRedirect(pathname: string): never {
+	const target = '/login?redirect=' + encodeURIComponent(pathname);
+	redirect(302, target);
+}
+
 export const handle: Handle = async ({ event, resolve }) => {
 	if (isPublicRoute(event.url.pathname)) {
 		return resolve(event);
@@ -20,14 +25,14 @@ export const handle: Handle = async ({ event, resolve }) => {
 
 	const sessionCookie = event.cookies.get('session');
 	if (!sessionCookie) {
-		redirect(302, '/login');
+		loginRedirect(event.url.pathname);
 	}
 
 	const api = apiClient(event.fetch);
 	const { data, error } = await api.GET('/v1/auth/me');
 
 	if (error || !data?.data) {
-		redirect(302, '/login');
+		loginRedirect(event.url.pathname);
 	}
 
 	const user = data.data;