feat(redesign): aurora foundation — tokens, glass sidebar, dashboard

Foundation pass on the Aurora redesign:

- app.css: full token swap to lavender/orchid/mint/sky pastel palette,
  vivid aurora gradient backdrop, frosted glass surface tokens, two
  themes (Aurora dark + Pearl light), shadow recipe for floating glass.
- fonts: add Geist Sans / Geist Mono / Newsreader, drop DM Sans usage
  (legacy fontsource entries kept in package.json until full migration).
- layout.svelte: sidebar becomes a floating glass rail with a conic-
  gradient brand orb, Newsreader italic 'Bridge' wordmark, soft glass
  hovers on nav links, gradient active indicator, gradient user avatar.
- Card.svelte: glass surface + inner highlight + soft hover lift.
- PageHeader.svelte: Newsreader serif display title.
- +page.svelte (dashboard): stat cards become glass with colored
  accent 'orb', event timeline gets soft glass rows + slide-on-hover.

Build clean (0 errors, pre-existing a11y warnings unchanged).
Other pages still inherit old chrome via shared tokens but will need
component-specific passes; tracked separately.

frontend/src/lib/components/PageHeader.svelte

@@ -1,16 +1,20 @@
 <script lang="ts">
-	let { title, description = '', children } = $props<{
+	import type { Snippet } from 'svelte';
+
+	interface Props {
 		title: string;
 		description?: string;
-		children?: import('svelte').Snippet;
-	}>();
+		children?: Snippet;
+	}
+
+	let { title, description = '', children }: Props = $props();
 </script>
 
-<div class="flex items-center justify-between mb-8">
+<div class="page-header">
 	<div class="animate-fade-slide-in">
-		<h2 class="text-2xl font-semibold tracking-tight">{title}</h2>
+		<h2 class="page-header__title">{title}</h2>
 		{#if description}
-			<p class="text-sm mt-1.5" style="color: var(--color-muted-foreground);">{description}</p>
+			<p class="page-header__desc">{description}</p>
 		{/if}
 	</div>
 	{#if children}
@@ -19,3 +23,29 @@
 		</div>
 	{/if}
 </div>
+
+<style>
+	.page-header {
+		display: flex;
+		align-items: center;
+		justify-content: space-between;
+		margin-bottom: 2rem;
+		gap: 1rem;
+		flex-wrap: wrap;
+	}
+	.page-header__title {
+		font-family: var(--font-display);
+		font-weight: 400;
+		font-size: 2.25rem;
+		letter-spacing: -0.025em;
+		line-height: 1.05;
+		color: var(--color-foreground);
+		margin: 0;
+	}
+	.page-header__desc {
+		font-size: 0.9rem;
+		color: var(--color-muted-foreground);
+		margin-top: 0.4rem;
+		line-height: 1.5;
+	}
+</style>