feat(timeline): add the "Ereignis hinzufügen" CTA to the Zeitstrahl header

Wrap the heading in a flex-wrap header so the gated add-event link drops
below the title at narrow widths instead of overflowing; the CTA targets
#781's /zeitstrahl/events/new and only shows for a WRITE_ALL viewer. Also
thread canWrite into TimelineView so a curator sees the edit pencils on
the real page. New i18n key timeline_add_event in de/en/es.

Refs #842
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/messages/de.json

@@ -1035,6 +1035,7 @@
 	"nav_geschichten": "Geschichten",
 	"nav_zeitstrahl": "Zeitstrahl",
 	"timeline_heading": "Zeitstrahl",
+	"timeline_add_event": "Ereignis hinzufügen",
 	"timeline_empty_state": "Noch keine Ereignisse.",
 	"timeline_undated_section": "Ohne Datum",
 	"timeline_unknown_person": "Unbekannt",

frontend/messages/en.json

@@ -1035,6 +1035,7 @@
 	"nav_geschichten": "Stories",
 	"nav_zeitstrahl": "Timeline",
 	"timeline_heading": "Timeline",
+	"timeline_add_event": "Add event",
 	"timeline_empty_state": "No events yet.",
 	"timeline_undated_section": "Without Date",
 	"timeline_unknown_person": "Unknown",

frontend/messages/es.json

@@ -1035,6 +1035,7 @@
 	"nav_geschichten": "Historias",
 	"nav_zeitstrahl": "Línea de tiempo",
 	"timeline_heading": "Línea de tiempo",
+	"timeline_add_event": "Añadir evento",
 	"timeline_empty_state": "Aún no hay eventos.",
 	"timeline_undated_section": "Sin Fecha",
 	"timeline_unknown_person": "Desconocido",

frontend/src/routes/zeitstrahl/+page.svelte

@@ -74,7 +74,20 @@ const metaLine = $derived.by(() => {
 	     border is intentionally omitted (the page is already bg-canvas), per the
 	     review of REQ-001 — the sheet reads through its padding, not a frame line. -->
 	<div data-testid="timeline-canvas" class="rounded-[10px] bg-canvas p-6">
-		<h1 class="font-serif text-2xl font-bold text-brand-navy">{m.timeline_heading()}</h1>
+		<!-- Wrapping header so the CTA drops below the heading at narrow widths
+		     (≤360px) instead of overflowing — #842 REQ-001. -->
+		<header class="flex flex-wrap items-center justify-between gap-3">
+			<h1 class="font-serif text-2xl font-bold text-brand-navy">{m.timeline_heading()}</h1>
+			{#if data.canWrite}
+				<a
+					data-testid="timeline-add-event"
+					href="/zeitstrahl/events/new"
+					class="inline-flex h-11 items-center rounded bg-primary px-4 font-sans text-sm font-medium text-primary-fg hover:opacity-90 focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring"
+				>
+					{m.timeline_add_event()}
+				</a>
+			{/if}
+		</header>
 		{#if hasContent}
 			<p data-testid="timeline-meta" class="mt-1 mb-6 font-sans text-xs text-ink-3">{metaLine}</p>
 			<TimelineFilters
@@ -99,7 +112,7 @@ const metaLine = $derived.by(() => {
 				</button>
 			</div>
 		{:else}
-			<TimelineView timeline={filteredTimeline} />
+			<TimelineView timeline={filteredTimeline} canWrite={data.canWrite} />
 		{/if}
 	</div>
 </div>

frontend/src/routes/zeitstrahl/page.svelte.spec.ts

@@ -213,3 +213,55 @@ describe('/zeitstrahl layer filter (#780)', () => {
 		await expect.element(meta).toHaveTextContent(m.timeline_events_count({ count: 2 }));
 	});
 });
+
+describe('/zeitstrahl curator affordances (#842)', () => {
+	const curated = (eventId: string) =>
+		makeEntry({
+			kind: 'EVENT',
+			type: 'PERSONAL',
+			derived: false,
+			eventId,
+			title: 'Auswanderung',
+			senderName: '',
+			receiverName: '',
+			documentId: undefined
+		});
+
+	const withWrite = (timeline: ReturnType<typeof makeTimelineDTO>) => ({
+		...pageData(timeline),
+		canWrite: true
+	});
+
+	it('renders the add-event CTA in a wrapping header when the viewer can write (REQ-001)', () => {
+		render(Page, { data: withWrite(makeTimelineDTO({ years: [makeYear(1909, [makeEntry()])] })) });
+		const add = document.querySelector(
+			'[data-testid="timeline-add-event"]'
+		) as HTMLAnchorElement | null;
+		expect(add).not.toBeNull();
+		expect(add?.getAttribute('href')).toBe('/zeitstrahl/events/new');
+		// The header wraps so the CTA drops below the heading at narrow widths (≤360px)
+		// rather than overflowing — REQ-001.
+		expect(add?.closest('header')?.classList.contains('flex-wrap')).toBe(true);
+	});
+
+	it('renders no add-event CTA when the viewer cannot write (REQ-002)', () => {
+		render(Page, {
+			data: pageData(makeTimelineDTO({ years: [makeYear(1909, [makeEntry()])] }))
+		});
+		expect(document.querySelector('[data-testid="timeline-add-event"]')).toBeNull();
+	});
+
+	it('threads canWrite to the timeline so a curator sees an event edit link (REQ-001/009)', () => {
+		render(Page, {
+			data: withWrite(makeTimelineDTO({ years: [makeYear(1924, [curated('p9')])] }))
+		});
+		expect(document.querySelector('a[href="/zeitstrahl/events/p9/edit"]')).not.toBeNull();
+	});
+
+	it('shows no event edit link to a reader (REQ-007)', () => {
+		render(Page, {
+			data: pageData(makeTimelineDTO({ years: [makeYear(1924, [curated('p9')])] }))
+		});
+		expect(document.querySelector('[data-testid="event-edit"]')).toBeNull();
+	});
+});