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)}
-					<li><LetterCard entry={entry} /></li>
+				<!-- The undated bucket is filtered from ALL entries, so it can hold
+				     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>