feat(briefwechsel): add ConversationThumbnail with aspect + page badge

Reads thumbnailAspect from the backend and swaps between a 120×168
portrait tile and a 168×120 landscape tile so postcards and photos
don't get cropped into a portrait frame. Shows a page-count badge
top-right for multi-page PDFs, and a pulsing skeleton while the
async thumbnail job hasn't run yet. URL assembly goes through the
existing thumbnailUrl helper so cache-busting stays consistent
with DocumentThumbnail.

Refs #305

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/lib/components/ConversationThumbnail.svelte.spec.ts

@@ -0,0 +1,110 @@
+import { describe, it, expect, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+
+import ConversationThumbnail from './ConversationThumbnail.svelte';
+
+afterEach(() => {
+	cleanup();
+});
+
+describe('ConversationThumbnail', () => {
+	it('renders the thumbnail image with a cache-busting v= query param', () => {
+		render(ConversationThumbnail, {
+			doc: {
+				id: '1111',
+				thumbnailKey: 'thumbnails/1111.jpg',
+				thumbnailGeneratedAt: '2026-04-10T09:00:00Z',
+				thumbnailAspect: 'PORTRAIT',
+				pageCount: 1
+			}
+		});
+
+		const img = document.querySelector('img') as HTMLImageElement | null;
+		expect(img).not.toBeNull();
+		expect(img!.getAttribute('src')).toContain('/api/documents/1111/thumbnail');
+		expect(img!.getAttribute('src')).toContain('v=');
+	});
+
+	it('uses portrait dimensions when aspect is PORTRAIT', () => {
+		render(ConversationThumbnail, {
+			doc: {
+				id: 'p1',
+				thumbnailKey: 'thumbnails/p1.jpg',
+				thumbnailAspect: 'PORTRAIT',
+				pageCount: 1
+			}
+		});
+
+		const tile = document.querySelector('[data-testid="conv-thumb-tile"]') as HTMLElement;
+		expect(tile.getAttribute('data-aspect')).toBe('PORTRAIT');
+	});
+
+	it('uses landscape dimensions when aspect is LANDSCAPE', () => {
+		render(ConversationThumbnail, {
+			doc: {
+				id: 'l1',
+				thumbnailKey: 'thumbnails/l1.jpg',
+				thumbnailAspect: 'LANDSCAPE',
+				pageCount: 1
+			}
+		});
+
+		const tile = document.querySelector('[data-testid="conv-thumb-tile"]') as HTMLElement;
+		expect(tile.getAttribute('data-aspect')).toBe('LANDSCAPE');
+	});
+
+	it('falls back to PORTRAIT when thumbnailAspect is missing', () => {
+		render(ConversationThumbnail, {
+			doc: {
+				id: 'n1',
+				thumbnailKey: 'thumbnails/n1.jpg'
+			}
+		});
+
+		const tile = document.querySelector('[data-testid="conv-thumb-tile"]') as HTMLElement;
+		expect(tile.getAttribute('data-aspect')).toBe('PORTRAIT');
+	});
+
+	it('renders the page badge when pageCount is greater than 1', () => {
+		render(ConversationThumbnail, {
+			doc: {
+				id: 'm1',
+				thumbnailKey: 'thumbnails/m1.jpg',
+				thumbnailAspect: 'PORTRAIT',
+				pageCount: 4
+			}
+		});
+
+		const badge = document.querySelector('[data-testid="conv-thumb-page-badge"]') as HTMLElement;
+		expect(badge).not.toBeNull();
+		expect(badge.textContent).toContain('4');
+	});
+
+	it('hides the page badge when pageCount is 1 or missing', () => {
+		render(ConversationThumbnail, {
+			doc: {
+				id: 's1',
+				thumbnailKey: 'thumbnails/s1.jpg',
+				thumbnailAspect: 'PORTRAIT',
+				pageCount: 1
+			}
+		});
+
+		const badge = document.querySelector('[data-testid="conv-thumb-page-badge"]');
+		expect(badge).toBeNull();
+	});
+
+	it('renders a skeleton placeholder when no thumbnailKey is set yet', () => {
+		render(ConversationThumbnail, {
+			doc: {
+				id: 'blank',
+				thumbnailAspect: 'PORTRAIT'
+			}
+		});
+
+		expect(document.querySelector('img')).toBeNull();
+		const skeleton = document.querySelector('[data-testid="conv-thumb-skeleton"]');
+		expect(skeleton).not.toBeNull();
+		expect(skeleton!.className).toContain('motion-safe:animate-pulse');
+	});
+});