test(admin): cover all import + thumbnail status branches

FAILED import-status with error message, RUNNING thumbnail with
progress count, RUNNING thumbnail without progress (total=0),
trigger thumbnail backfill, trigger import from idle.

5 new tests covering ~10 branches.

Refs #496.

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

frontend/src/routes/admin/system/page.svelte.test.ts

@@ -238,4 +238,114 @@ describe('admin/system page', () => {
 		const banner = document.querySelector('[data-testid="thumbnails-status-done"]');
 		expect(banner).not.toBeNull();
 	});
+
+	it('renders the FAILED state for import-status with retry button', async () => {
+		fetchSpy.mockImplementation(async (url: RequestInfo | URL) => {
+			const u = url.toString();
+			if (u.includes('import-status')) {
+				return new Response(
+					JSON.stringify({
+						state: 'FAILED',
+						message: 'database error',
+						processed: 0,
+						startedAt: null
+					}),
+					{ status: 200, headers: { 'Content-Type': 'application/json' } }
+				);
+			}
+			return new Response(JSON.stringify({ state: 'IDLE' }), {
+				status: 200,
+				headers: { 'Content-Type': 'application/json' }
+			});
+		});
+
+		render(AdminSystemPage, { props: {} });
+
+		await new Promise((r) => setTimeout(r, 100));
+		expect(document.body.textContent).toContain('database error');
+	});
+
+	it('renders the running thumbnail status with progress count', async () => {
+		fetchSpy.mockImplementation(async (url: RequestInfo | URL) => {
+			const u = url.toString();
+			if (u.includes('thumbnail-status')) {
+				return new Response(
+					JSON.stringify({
+						state: 'RUNNING',
+						message: '',
+						total: 100,
+						processed: 30,
+						skipped: 5,
+						failed: 1,
+						startedAt: null
+					}),
+					{ status: 200, headers: { 'Content-Type': 'application/json' } }
+				);
+			}
+			return new Response(JSON.stringify({ state: 'IDLE' }), {
+				status: 200,
+				headers: { 'Content-Type': 'application/json' }
+			});
+		});
+
+		render(AdminSystemPage, { props: {} });
+
+		await new Promise((r) => setTimeout(r, 100));
+		// Total 100, processed+skipped+failed = 36
+		expect(document.body.textContent).toMatch(/36|100/);
+	});
+
+	it('triggers thumbnail backfill when its button is clicked', async () => {
+		render(AdminSystemPage, { props: {} });
+
+		await new Promise((r) => setTimeout(r, 50));
+		const btns = Array.from(document.querySelectorAll('[data-thumbnails-trigger]'));
+		(btns[0] as HTMLButtonElement)?.click();
+
+		await new Promise((r) => setTimeout(r, 50));
+		const calls = fetchSpy.mock.calls.map((c) => c[0].toString());
+		expect(calls.some((c) => c.includes('generate-thumbnails'))).toBe(true);
+	});
+
+	it('triggers import when import button is clicked from idle state', async () => {
+		render(AdminSystemPage, { props: {} });
+
+		await new Promise((r) => setTimeout(r, 50));
+		const btns = Array.from(document.querySelectorAll('[data-import-trigger]'));
+		(btns[0] as HTMLButtonElement)?.click();
+
+		await new Promise((r) => setTimeout(r, 50));
+		const calls = fetchSpy.mock.calls.map((c) => c[0].toString());
+		expect(calls.some((c) => c.includes('trigger-import'))).toBe(true);
+	});
+
+	it('renders the running thumbnail status without progress when total is 0', async () => {
+		fetchSpy.mockImplementation(async (url: RequestInfo | URL) => {
+			const u = url.toString();
+			if (u.includes('thumbnail-status')) {
+				return new Response(
+					JSON.stringify({
+						state: 'RUNNING',
+						message: '',
+						total: 0,
+						processed: 0,
+						skipped: 0,
+						failed: 0,
+						startedAt: null
+					}),
+					{ status: 200, headers: { 'Content-Type': 'application/json' } }
+				);
+			}
+			return new Response(JSON.stringify({ state: 'IDLE' }), {
+				status: 200,
+				headers: { 'Content-Type': 'application/json' }
+			});
+		});
+
+		render(AdminSystemPage, { props: {} });
+
+		await new Promise((r) => setTimeout(r, 100));
+		// running state shown but no progress count when total=0
+		expect(document.body.textContent).toMatch(/läuft|wird|generier/i);
+	});
 });