refactor(timeline): drop EventForm's redundant type state

The submitted type comes from EventTypeSelect's own hidden input; EventForm's
`type` $state was only read to seed `value=` and the onchange reassignment
had no downstream reader. Inline the seed expression and pass markDirty
directly, removing the second source of truth.

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

frontend/src/lib/timeline/EventForm.svelte

@@ -61,7 +61,6 @@ let {
 // won't update the form — the two dedicated routes always remount, which is fine.
 let title = $state(form?.title ?? event?.title ?? '');
 let description = $state(form?.description ?? event?.description ?? '');
-let type = $state<string>(form?.type ?? event?.type ?? 'PERSONAL');
 let dateIso = $state(form?.eventDate ?? event?.eventDate ?? '');
 let precision = $state<DatePrecision>(
 	(form?.precision as DatePrecision) ?? (event?.precision as DatePrecision) ?? 'DAY'
@@ -212,10 +211,11 @@ function markDirty() {
 						<span class="mb-1 block text-sm font-medium text-ink-2"
 							>{m.event_editor_type_label()}</span
 						>
-						<EventTypeSelect value={type} name="type" onchange={(t) => {
-								type = t;
-								markDirty();
-							}} />
+						<EventTypeSelect
+							value={form?.type ?? event?.type ?? 'PERSONAL'}
+							name="type"
+							onchange={markDirty}
+						/>
 					</div>
 
 					<div class="grid grid-cols-1 gap-5 md:grid-cols-2">

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

@@ -62,6 +62,20 @@ describe('EventForm — date precision RANGE reveal (headline AC, REQ-008/009)',
 	});
 });
 
+describe('EventForm — type seeding (review #8 refactor fence)', () => {
+	it('seeds the type selector from the event so the submitted type is correct', async () => {
+		renderForm({ event: makeEvent({ type: 'HISTORICAL' }) });
+		const hidden = document.querySelector('input[type="hidden"][name="type"]') as HTMLInputElement;
+		expect(hidden.value).toBe('HISTORICAL');
+	});
+
+	it('prefers the fail-payload type over the seeded event', async () => {
+		renderForm({ event: makeEvent({ type: 'PERSONAL' }), form: { type: 'HISTORICAL' } });
+		const hidden = document.querySelector('input[type="hidden"][name="type"]') as HTMLInputElement;
+		expect(hidden.value).toBe('HISTORICAL');
+	});
+});
+
 describe('EventForm — picker preselect (REQ-014)', () => {
 	it('preselects a person when initialPersons is provided', async () => {
 		renderForm({ initialPersons: [{ id: 'p1', displayName: 'Anna Müller' }] });