fix(login): remove py-6 padding from layout on auth pages to prevent scrolling

The global layout wrapped all pages in <main class="py-6">, adding 48px
of vertical padding. Combined with min-h-screen on the login page div,
the total height exceeded 100vh and made the page scrollable.

Auth pages (/login, /forgot-password, /reset-password) now get no
padding from the layout — the same path check already used to hide
the nav header.

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

frontend/src/routes/+layout.svelte

@@ -24,6 +24,10 @@ onMount(() => {
 	hydrated = true;
 });
 
+const isAuthPage = $derived(
+	['/login', '/forgot-password', '/reset-password'].some((p) => page.url.pathname.startsWith(p))
+);
+
 let userMenuOpen = $state(false);
 
 const userInitials = $derived.by(() => {
@@ -47,7 +51,7 @@ function clickOutside(node: HTMLElement) {
 </script>
 
 <div class="min-h-screen bg-canvas" data-hydrated={hydrated || undefined}>
-	{#if !['/login', '/forgot-password', '/reset-password'].some((p) => page.url.pathname.startsWith(p))}
+	{#if !isAuthPage}
 		<header class="sticky top-0 z-50 border-b border-line-2 bg-surface">
 			<!-- De Gruyter Brill purple accent strip -->
 			<div class="h-1 bg-brand-purple"></div>
@@ -194,7 +198,7 @@ function clickOutside(node: HTMLElement) {
 		</header>
 	{/if}
 
-	<main class="py-6">
+	<main class={isAuthPage ? '' : 'py-6'}>
 		{@render children()}
 	</main>
 </div>