story-ui-job-list-error: test error display on job list page

Add SSR-based component test verifying error display logic from
+page.svelte. Uses svelte/server render() to avoid mount/browser
requirements.

- JobErrorDisplay.svelte: test component replicating error display template
- app-environment.ts: mock for /environment (needed by accent.ts)
- job-list-error-display.test.ts: 5 tests covering:
  * failed job with error -> error text rendered
  * done job with null error -> no error text
  * failed job with null error -> no error text
  * non-failed status with error -> no error text
  * title attribute contains full error text
- vitest.config.ts: add svelte() plugin for .svelte file transforms,
  add /environment alias for test mocking

Tests: 237 passed (19 files), 0 type errors, build OK.

vitest.config.ts

@@ -1,7 +1,9 @@
 import { defineConfig } from 'vitest/config';
+import { svelte } from '@sveltejs/vite-plugin-svelte';
 import path from 'path';
 
 export default defineConfig({
+	plugins: [svelte()],
 	test: {
 		environment: 'node',
 		globals: true,
@@ -15,7 +17,8 @@ export default defineConfig({
 	},
 	resolve: {
 		alias: {
-			'$lib': path.resolve('./src/lib')
+			'$lib': path.resolve('./src/lib'),
+			'$app/environment': path.resolve('./src/tests/__mocks__/app-environment.ts'),
 		}
 	}
 });