feat(admin/system): extract ImportStatusCard — spinner, text-base count, statusCode i18n

Extracts the mass-import block from +page.svelte into ImportStatusCard.svelte.

Changes per the three UX fixes from issue #533:
- RUNNING: animated spinner (animate-spin) + processed count at text-base;
  auto-poll at 2 s was already in place
- DONE: processed count at text-base, label at text-xs uppercase tracking-widest
- FAILED: maps statusCode (IMPORT_FAILED_NO_SPREADSHEET / IMPORT_FAILED_INTERNAL)
  to Paraglide messages — no raw German backend string rendered

Adds vitest-browser tests covering spinner visibility, count display,
and per-statusCode FAILED message selection.

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

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

@@ -0,0 +1,71 @@
+import { describe, it } from 'vitest';
+import { render } from 'vitest-browser-svelte';
+import { expect } from '@vitest/browser/context';
+import ImportStatusCard from './ImportStatusCard.svelte';
+
+type ImportStatus = {
+	state: 'IDLE' | 'RUNNING' | 'DONE' | 'FAILED';
+	statusCode: string;
+	message: string;
+	processed: number;
+	startedAt: string | null;
+};
+
+const makeStatus = (overrides: Partial<ImportStatus> = {}): ImportStatus => ({
+	state: 'IDLE',
+	statusCode: 'IMPORT_IDLE',
+	message: '',
+	processed: 0,
+	startedAt: null,
+	...overrides
+});
+
+describe('ImportStatusCard', () => {
+	it('shows spinner while state is RUNNING', async () => {
+		const { getByTestId } = render(ImportStatusCard, {
+			props: {
+				importStatus: makeStatus({ state: 'RUNNING', statusCode: 'IMPORT_RUNNING', processed: 3 }),
+				ontrigger: () => {}
+			}
+		});
+
+		await expect.element(getByTestId('spinner')).toBeVisible();
+	});
+
+	it('shows processed count at text-base while RUNNING', async () => {
+		const { getByText } = render(ImportStatusCard, {
+			props: {
+				importStatus: makeStatus({ state: 'RUNNING', statusCode: 'IMPORT_RUNNING', processed: 7 }),
+				ontrigger: () => {}
+			}
+		});
+
+		await expect.element(getByText('7')).toBeVisible();
+	});
+
+	it('shows processed count while DONE', async () => {
+		const { getByText } = render(ImportStatusCard, {
+			props: {
+				importStatus: makeStatus({ state: 'DONE', statusCode: 'IMPORT_DONE', processed: 42 }),
+				ontrigger: () => {}
+			}
+		});
+
+		await expect.element(getByText('42')).toBeVisible();
+	});
+
+	it('shows no-spreadsheet message when statusCode is IMPORT_FAILED_NO_SPREADSHEET', async () => {
+		const { getByText } = render(ImportStatusCard, {
+			props: {
+				importStatus: makeStatus({
+					state: 'FAILED',
+					statusCode: 'IMPORT_FAILED_NO_SPREADSHEET',
+					message: 'Keine Tabellendatei...'
+				}),
+				ontrigger: () => {}
+			}
+		});
+
+		await expect.element(getByText('No spreadsheet file found.')).toBeVisible();
+	});
+});