fix(person-typeahead): add resetKey prop to clear term on navigation reset

When the user types in the sender/receiver typeahead without selecting a
person and then clicks ×-reset (navigating back to /documents), the
manually-typed term was not cleared because initialName stayed '' between
navigations — the existing $effect tracking initialName never fired.

Adding `resetKey` (incremented by the page on every navigation) forces
the effect to re-run via `void resetKey`, clearing searchTerm=initialName
even when initialName is unchanged.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/person/PersonTypeahead.svelte

@@ -21,6 +21,7 @@ interface Props {
 	restrictToCorrespondentsOf?: string;
 	excludePersonId?: string;
 	badge?: 'additive' | 'replace';
+	resetKey?: number;
 	onchange?: (value: string) => void;
 	onfocused?: () => void;
 }
@@ -39,6 +40,7 @@ let {
 	restrictToCorrespondentsOf,
 	excludePersonId,
 	badge,
+	resetKey = 0,
 	onchange,
 	onfocused
 }: Props = $props();
@@ -48,8 +50,11 @@ let {
 // eslint-disable-next-line svelte/prefer-writable-derived
 let searchTerm = $state(initialName);
 
-// Sync display text when the selected person changes externally (e.g. swap, navigation).
+// Sync display text when initialName changes OR when resetKey increments (navigation reset).
+// resetKey is incremented by the page on every SvelteKit navigation so that a manually-typed
+// term that was never committed (no person selected) gets cleared even if initialName stays ''.
 $effect(() => {
+	void resetKey;
 	searchTerm = initialName;
 });
 

frontend/src/lib/person/PersonTypeahead.svelte.spec.ts

@@ -270,6 +270,30 @@ describe('PersonTypeahead – correspondent mode', () => {
 	});
 });
 
+// ─── resetKey ─────────────────────────────────────────────────────────────────
+
+describe('PersonTypeahead – resetKey', () => {
+	it('clears a manually-typed term when resetKey changes even if initialName stays empty', async () => {
+		mockFetchWithPersons([]);
+		const { rerender } = render(PersonTypeahead, {
+			name: 'senderId',
+			label: 'Absender',
+			initialName: '',
+			resetKey: 0
+		});
+		const input = page.getByPlaceholder('Namen tippen...');
+
+		// User types something without selecting a person
+		await input.fill('Max');
+		await waitForDebounce();
+		await expect.element(input).toHaveValue('Max');
+
+		// Navigation resets: initialName stays '', but resetKey increments
+		await rerender({ name: 'senderId', label: 'Absender', initialName: '', resetKey: 1 });
+		await expect.element(input).toHaveValue('');
+	});
+});
+
 // ─── Click outside ────────────────────────────────────────────────────────────
 
 describe('PersonTypeahead – click outside', () => {