test(admin): expand admin/system page coverage

Adds backfill-versions and backfill-file-hashes click handlers,
verifies initial fetch hits import-status and thumbnail-status.

3 new tests targeting ~10 branches in the page component.

Refs #496.

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

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

@@ -1,4 +1,4 @@
-import { describe, it, expect, afterEach } from 'vitest';
+import { describe, it, expect, vi, afterEach, beforeEach } from 'vitest';
 import { cleanup, render } from 'vitest-browser-svelte';
 import { page } from 'vitest/browser';
 import AdminSystemPage from './+page.svelte';
@@ -6,6 +6,28 @@ import AdminSystemPage from './+page.svelte';
 afterEach(cleanup);
 
 describe('admin/system page', () => {
+	let fetchSpy: ReturnType<typeof vi.spyOn>;
+
+	beforeEach(() => {
+		fetchSpy = vi.spyOn(globalThis, 'fetch').mockResolvedValue(
+			new Response(
+				JSON.stringify({
+					state: 'IDLE',
+					message: '',
+					total: 0,
+					processed: 0,
+					skipped: 0,
+					failed: 0
+				}),
+				{ status: 200, headers: { 'Content-Type': 'application/json' } }
+			)
+		);
+	});
+
+	afterEach(() => {
+		fetchSpy?.mockRestore();
+	});
+
 	it('renders the backfill versions card', async () => {
 		render(AdminSystemPage, { props: {} });
 
@@ -46,4 +68,46 @@ describe('admin/system page', () => {
 		const banners = document.querySelectorAll('.bg-green-50');
 		expect(banners.length).toBe(0);
 	});
+
+	it('triggers backfill versions when its button is clicked', async () => {
+		fetchSpy.mockResolvedValueOnce(
+			new Response(JSON.stringify({ count: 7 }), {
+				status: 200,
+				headers: { 'Content-Type': 'application/json' }
+			})
+		);
+
+		render(AdminSystemPage, { props: {} });
+
+		const btn = (await page
+			.getByRole('button', { name: /jetzt auffüllen/i })
+			.element()) as HTMLButtonElement;
+		btn.click();
+
+		await new Promise((r) => setTimeout(r, 50));
+		const calls = fetchSpy.mock.calls.map((c) => c[0].toString());
+		expect(calls.some((c) => c.includes('backfill-versions'))).toBe(true);
+	});
+
+	it('triggers file-hashes backfill when its button is clicked', async () => {
+		render(AdminSystemPage, { props: {} });
+
+		const btn = (await page
+			.getByRole('button', { name: /datei-hashes berechnen/i })
+			.element()) as HTMLButtonElement;
+		btn.click();
+
+		await new Promise((r) => setTimeout(r, 50));
+		const calls = fetchSpy.mock.calls.map((c) => c[0].toString());
+		expect(calls.some((c) => c.includes('backfill-file-hashes'))).toBe(true);
+	});
+
+	it('initial fetch loads import-status and thumbnail-status', async () => {
+		render(AdminSystemPage, { props: {} });
+
+		await new Promise((r) => setTimeout(r, 50));
+		const calls = fetchSpy.mock.calls.map((c) => c[0].toString());
+		expect(calls.some((c) => c.includes('import-status'))).toBe(true);
+		expect(calls.some((c) => c.includes('thumbnail-status'))).toBe(true);
+	});
 });