refactor(timeline): drop the canvas outer border (REQ-001)

The page is already bg-canvas, so the frame's border was the only thing
making it visible; per review it reads cleaner without it. Keep the padded
bg-canvas surface; the timeline sits on the page without a frame line.

Refs #833
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -30,9 +30,10 @@ const metaLine = $derived.by(() => {
 </svelte:head>
 
 <div class="mx-auto max-w-5xl px-4 py-8">
-	<!-- The .tl-canvas sheet: a framed surface the timeline reads as a finished
-	     life-thread rather than bare page chrome (REQ-001). -->
-	<div data-testid="timeline-canvas" class="rounded-[10px] border border-line bg-canvas p-6">
+	<!-- The .tl-canvas sheet: a padded canvas surface for the timeline. The outer
+	     border is intentionally omitted (the page is already bg-canvas), per the
+	     review of REQ-001 — the sheet reads through its padding, not a frame line. -->
+	<div data-testid="timeline-canvas" class="rounded-[10px] bg-canvas p-6">
 		<h1 class="font-serif text-2xl font-bold text-brand-navy">{m.timeline_heading()}</h1>
 		{#if hasContent}
 			<p data-testid="timeline-meta" class="mt-1 mb-6 font-sans text-xs text-ink-3">{metaLine}</p>

frontend/src/routes/zeitstrahl/page.svelte.spec.ts

@@ -29,15 +29,16 @@ const pageData = (timeline: ReturnType<typeof makeTimelineDTO>) => ({
 });
 
 describe('/zeitstrahl page', () => {
-	it('wraps the timeline in a bordered, rounded canvas frame (REQ-001)', () => {
+	it('wraps the timeline in a padded canvas surface, without an outer border (REQ-001)', () => {
 		render(Page, {
 			data: pageData(makeTimelineDTO({ years: [makeYear(1909, [makeEntry()])] }))
 		});
 		const canvas = document.querySelector('[data-testid="timeline-canvas"]');
 		expect(canvas).not.toBeNull();
 		expect(canvas?.classList.contains('bg-canvas')).toBe(true);
-		expect(canvas?.classList.contains('border')).toBe(true);
-		// the timeline renders inside the frame
+		// The outer border was dropped in review (the page is already bg-canvas).
+		expect(canvas?.classList.contains('border')).toBe(false);
+		// the timeline renders inside the surface
 		expect(canvas?.querySelector('ol')).not.toBeNull();
 	});