fix(search): tagQ alone now triggers search mode; selecting chip clears tagQ

- isDashboard was ignoring tagQ so typing in tag filter showed dashboard
- addTag now calls onTextInput('') to clear tagQ when a chip is selected

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

frontend/src/lib/components/TagInput.svelte

@@ -44,6 +44,7 @@ function addTag(tag: string) {
 	suggestions = [];
 	showSuggestions = false;
 	activeIndex = -1;
+	onTextInput?.('');
 }
 
 function removeTag(index: number) {

frontend/src/lib/components/TagInput.svelte.spec.ts

@@ -228,4 +228,16 @@ describe('TagInput – onTextInput callback', () => {
 		const input = page.getByRole('textbox');
 		await expect(input.fill('fa')).resolves.not.toThrow();
 	});
+
+	it('calls onTextInput with empty string when a tag chip is added', async () => {
+		mockFetchWithTags(['Kaufvertrag']);
+		const onTextInput = vi.fn();
+		render(TagInput, { tags: [], allowCreation: false, onTextInput });
+		const input = page.getByRole('textbox');
+		await input.fill('Ka');
+		await waitForDebounce();
+		const option = page.getByRole('option', { name: 'Kaufvertrag' });
+		await option.click();
+		await expect.poll(() => onTextInput.mock.calls.at(-1)).toEqual(['']);
+	});
 });