feat(timeline): give LetterCard an event variant and chip suppression

Add a `variant="event"` that marks the card `.lcard.ev` for Ereignis-mode event
clusters (#827, REQ-014) and a `suppressTagChip` that hides the per-letter
TagChip inside its own Thema bucket where the header already conveys the topic
(REQ-017). Datum/Ereignis keep the #838 per-letter chip behaviour.

Refs #827
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -127,3 +127,28 @@ describe('LetterCard', () => {
 		expect(chip?.textContent).toContain('Familie');
 	});
 });
+
+describe('LetterCard — grouping variants (#827, REQ-014/017)', () => {
+	it('carries the .lcard.ev class in the event variant (REQ-014)', () => {
+		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-014)', () => {
+		render(LetterCard, { entry: makeEntry() });
+		expect(document.querySelector('a.ev')).toBeNull();
+	});
+
+	it('suppresses the per-letter tag chip when asked, even with a root tag (REQ-017)', () => {
+		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 — Datum/Ereignis (REQ-017)', () => {
+		render(LetterCard, { entry: makeEntry({ rootTagName: 'Krieg', rootTagColor: 'sienna' }) });
+		expect(document.querySelector('[data-testid="tag-chip"]')).not.toBeNull();
+	});
+});