fix(#96): remove off-brand lavender accent bar from all pages

The h-1 bg-brand-purple strip (#b4b9ff) is not a De Gruyter brand
color and was added as a rough placeholder. Removed from +layout.svelte
and the three auth pages (login, forgot-password, reset-password).
Also removed the unused --palette-purple and --color-brand-purple CSS
tokens from layout.css.

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

frontend/src/routes/+layout.svelte

@@ -39,9 +39,6 @@ const userInitials = $derived.by(() => {
 <div class="min-h-screen bg-canvas" data-hydrated={hydrated || undefined}>
 	{#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>
-
 			<div class="mx-auto max-w-7xl px-4 sm:px-6 lg:px-8">
 				<div class="flex h-16 justify-between">
 					<!-- Logo & Nav -->

frontend/src/routes/forgot-password/+page.svelte

@@ -5,9 +5,6 @@ let { form }: { form?: { error?: string; success?: boolean } } = $props();
 </script>
 
 <div class="relative flex min-h-screen flex-col bg-surface">
-	<!-- Accent strip -->
-	<div class="h-1 bg-brand-purple"></div>
-
 	<div class="flex flex-1 items-center justify-center px-4">
 		<div class="w-full max-w-sm">
 			<!-- Logo -->

frontend/src/routes/layout.css

@@ -10,7 +10,6 @@
 	--palette-mint: #a1dcd8;
 	--palette-turquoise: #00c7b1;
 	--palette-sand: #f0efe9;
-	--palette-purple: #b4b9ff;
 
 	/* Typography */
 	--font-sans: 'Montserrat', ui-sans-serif, system-ui, sans-serif;
@@ -58,7 +57,6 @@
 	--color-pdf-text: var(--c-pdf-text);
 
 	/* Static brand tokens (not themed) */
-	--color-brand-purple: var(--palette-purple);
 	--color-brand-navy: var(--palette-navy);
 	--color-brand-mint: var(--palette-mint);
 }

frontend/src/routes/login/+page.svelte

@@ -10,9 +10,6 @@ const activeLocale = $derived(getLocale().toUpperCase());
 </script>
 
 <div class="relative flex min-h-screen flex-col bg-canvas">
-	<!-- DGB purple accent strip -->
-	<div class="h-1 bg-brand-purple"></div>
-
 	<!-- Language switcher -->
 	<div class="absolute top-4 right-4 flex items-center gap-1">
 		{#each locales as locale (locale)}

frontend/src/routes/reset-password/+page.svelte

@@ -12,9 +12,6 @@ let {
 </script>
 
 <div class="relative flex min-h-screen flex-col bg-surface">
-	<!-- Accent strip -->
-	<div class="h-1 bg-brand-purple"></div>
-
 	<div class="flex flex-1 items-center justify-center px-4">
 		<div class="w-full max-w-sm">
 			<!-- Logo -->