fix(timeline): render undated events as pills/bands, not letter cards

The undated bucket is assembled from all entries, so it can contain
events as well as letters. Rendering every undated entry with LetterCard
produced a dead /documents/undefined link and "Unknown -> Unknown" for
events. Dispatch on kind/type like YearBand does (WorldBand/EventPill/
LetterCard).

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

frontend/src/lib/timeline/TimelineView.svelte

@@ -3,6 +3,9 @@ import * as m from '$lib/paraglide/messages.js';
 import YearBand from './YearBand.svelte';
 import GapSpan from './GapSpan.svelte';
 import LetterCard from './LetterCard.svelte';
+import EventPill from './EventPill.svelte';
+import WorldBand from './WorldBand.svelte';
+import { entryKey } from './entryKey';
 import type { components } from '$lib/generated/api';
 
 type TimelineDTO = components['schemas']['TimelineDTO'];
@@ -59,8 +62,22 @@ const isEmpty = $derived(timeline.years.length === 0 && timeline.undated.length
 		<section data-testid="undated-section" class="mx-auto mt-8 max-w-3xl">
 			<h2 class="mb-3 font-serif text-sm font-bold text-ink-2">{m.timeline_undated_section()}</h2>
 			<ul class="space-y-2">
-				{#each timeline.undated as entry (entry.documentId ?? entry.title)}
+				<!-- The undated bucket is filtered from ALL entries, so it can hold
-					<li><LetterCard entry={entry} /></li>
+				     events as well as letters. Dispatch on kind/type exactly like
+				     YearBand — an event rendered as a LetterCard would link to
+				     /documents/undefined and read "Unknown → Unknown" (REQ-007/008/009). -->
+				{#each timeline.undated as entry (entryKey(entry))}
+					<li>
+						{#if entry.kind === 'EVENT'}
+							{#if entry.type === 'HISTORICAL'}
+								<WorldBand entry={entry} />
+							{:else}
+								<EventPill entry={entry} />
+							{/if}
+						{:else}
+							<LetterCard entry={entry} />
+						{/if}
+					</li>
 				{/each}
 			</ul>
 		</section>

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

@@ -89,6 +89,70 @@ describe('TimelineView', () => {
 		expect(document.querySelector('[data-testid="undated-section"]')).not.toBeNull();
 	});
 
+	it('renders an undated curated EVENT as a pill, not a broken letter card (REQ-008/016)', () => {
+		render(TimelineView, {
+			timeline: makeTimelineDTO({
+				undated: [
+					makeEntry({
+						kind: 'EVENT',
+						type: 'PERSONAL',
+						derived: false,
+						eventId: 'e1',
+						precision: 'UNKNOWN',
+						eventDate: undefined,
+						title: 'Auswanderung',
+						senderName: '',
+						receiverName: '',
+						documentId: undefined
+					})
+				]
+			})
+		});
+		// The event renders inside the undated section…
+		expect(document.querySelector('[data-testid="undated-section"]')).not.toBeNull();
+		expect(document.body.textContent).toContain('Auswanderung');
+		// …as an EventPill (its edit affordance), never as a letter card linking
+		// to /documents/undefined with "Unbekannt → Unbekannt".
+		expect(document.querySelector('[data-testid="event-edit"]')).not.toBeNull();
+		expect(document.querySelector('a[href="/documents/undefined"]')).toBeNull();
+		expect(document.body.textContent).not.toContain('Unbekannt');
+	});
+
+	it('renders an undated HISTORICAL EVENT as a world band, not a letter card (REQ-009/016)', () => {
+		render(TimelineView, {
+			timeline: makeTimelineDTO({
+				undated: [
+					makeEntry({
+						kind: 'EVENT',
+						type: 'HISTORICAL',
+						derived: false,
+						precision: 'UNKNOWN',
+						eventDate: undefined,
+						title: 'Weltwirtschaftskrise',
+						senderName: '',
+						receiverName: '',
+						documentId: undefined
+					})
+				]
+			})
+		});
+		expect(document.querySelector('[data-testid="undated-section"]')).not.toBeNull();
+		expect(document.body.textContent).toContain('Weltwirtschaftskrise');
+		// HISTORICAL → WorldBand carries the sr-only "Weltgeschehen" cue (REQ-018),
+		// not a broken document link.
+		expect(document.body.textContent).toContain('Weltgeschehen');
+		expect(document.querySelector('a[href="/documents/undefined"]')).toBeNull();
+	});
+
+	it('still renders an undated LETTER as a letter card (REQ-016)', () => {
+		render(TimelineView, {
+			timeline: makeTimelineDTO({
+				undated: [makeEntry({ precision: 'UNKNOWN', eventDate: undefined, documentId: 'u1' })]
+			})
+		});
+		expect(document.querySelector('a[href="/documents/u1"]')).not.toBeNull();
+	});
+
 	it('renders two derived events in one band without key collision (no-double-null-key)', () => {
 		const a = makeEntry({
 			kind: 'EVENT',