fix(timeline): skip empty-title events in the cluster lookup

A titleless or whitespace-only event stored `''` in the lookup, so its
letters still clustered and rendered a label-less `✉` mystery card. The
lookup now skips events whose trimmed title is empty — those letters stay
loose. Fixes review finding #8.

Refs #850
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/timeline/eventClustering.spec.ts

@@ -59,6 +59,22 @@ describe('eventClustering — buildEventLookup', () => {
 		expect(lookup.has(EV_A)).toBe(false);
 		expect(lookup.size).toBe(0);
 	});
+
+	it('skips an event with an empty or whitespace title — no bare ✉ card (#8)', () => {
+		const timeline: TimelineDTO = {
+			years: [
+				{
+					year: 1916,
+					entries: [
+						makeEvent({ eventId: EV_A, title: '' }),
+						makeEvent({ eventId: EV_B, title: '   ' })
+					]
+				}
+			],
+			undated: []
+		};
+		expect(buildEventLookup(timeline).size).toBe(0);
+	});
 });
 
 describe('eventClustering — splitYearLetters', () => {

frontend/src/lib/timeline/eventClustering.ts

@@ -33,13 +33,17 @@ export interface SplitLetters {
  * Only year-band events are collected: an undated event renders as a plain pill in the undated
  * bucket (out of clustering scope), so including it would scatter its dated letters into orphaned
  * cross-year cards detached from that pill (#7).
+ *
+ * An event with an empty/whitespace title is skipped too — clustering under it would render a
+ * label-less `✉` mystery card; its letters stay loose instead (#8).
  */
 export function buildEventLookup(timeline: TimelineDTO): Map<string, string> {
 	const lookup = new Map<string, string>();
 	const collect = (entries: TimelineEntryDTO[]) => {
 		for (const entry of entries) {
-			if (entry.kind === 'EVENT' && entry.eventId && entry.type !== 'HISTORICAL') {
-				lookup.set(entry.eventId, entry.title ?? '');
+			const title = entry.title?.trim();
+			if (entry.kind === 'EVENT' && entry.eventId && entry.type !== 'HISTORICAL' && title) {
+				lookup.set(entry.eventId, title);
 			}
 		}
 	};