feat(timeline): add compact + event variants to LetterCard

The event variant adds the .lcard.ev marker for letters living inside a
contained event card; the compact variant tightens the row (py-1, text-xs
title) and drops the redundant date chip when the title already embeds the
date. suppressTagChip lets a caller that already conveys the topic hide the
per-letter root-tag chip. Plain Datum letters are unchanged.

Refs #850

frontend/src/lib/timeline/LetterCard.svelte.spec.ts

@@ -127,3 +127,46 @@ describe('LetterCard', () => {
 		expect(chip?.textContent).toContain('Familie');
 	});
 });
+
+describe('LetterCard — event-cluster variants (#850, REQ-002)', () => {
+	it('carries the .lcard.ev class in the event variant (REQ-002)', () => {
+		render(LetterCard, { entry: makeEntry(), variant: 'event' });
+		expect(document.querySelector('a.lcard.ev')).not.toBeNull();
+	});
+
+	it('is a plain card with no .ev marker by default (REQ-006)', () => {
+		render(LetterCard, { entry: makeEntry() });
+		expect(document.querySelector('a.ev')).toBeNull();
+	});
+
+	it('suppresses the per-letter tag chip when asked, even with a root tag', () => {
+		render(LetterCard, {
+			entry: makeEntry({ rootTagName: 'Krieg', rootTagColor: 'sienna' }),
+			suppressTagChip: true
+		});
+		expect(document.querySelector('[data-testid="tag-chip"]')).toBeNull();
+	});
+
+	it('still shows the per-letter tag chip when not suppressed', () => {
+		render(LetterCard, { entry: makeEntry({ rootTagName: 'Krieg', rootTagColor: 'sienna' }) });
+		expect(document.querySelector('[data-testid="tag-chip"]')).not.toBeNull();
+	});
+
+	it('drops the redundant date line in the compact variant when a title is present (#850)', () => {
+		// Inside an event card the year already frames the time, and these archive titles
+		// embed the date — so the compact in-card letter omits the date chip.
+		render(LetterCard, { entry: makeEntry({ title: 'H-0023 – 6. Juli 1916' }), compact: true });
+		expect(document.querySelector('[data-testid="letter-date"]')).toBeNull();
+		expect(document.body.textContent).toContain('Karl Raddatz'); // sender still shown
+	});
+
+	it('keeps the date in the compact variant when the letter has no title (#850)', () => {
+		render(LetterCard, { entry: makeEntry({ title: undefined }), compact: true });
+		expect(document.querySelector('[data-testid="letter-date"]')).not.toBeNull();
+	});
+
+	it('renders the compact variant on a single tighter row (#850)', () => {
+		render(LetterCard, { entry: makeEntry(), compact: true });
+		expect(document.querySelector('a.lcard.compact')).not.toBeNull();
+	});
+});