Clarify download states and make the empty page useful

frontend/downloads-page.test.js

@@ -0,0 +1,50 @@
+const { test } = require('node:test');
+const assert = require('node:assert/strict');
+const DownloadsPage = require('./downloads-page.js');
+
+test('groupJobs categorizes active, queued, paused, and failed jobs correctly', () => {
+  const jobs = [
+    { id: '1', title: 'Job 1', status: 'active' },
+    { id: '2', title: 'Job 2', status: 'queued' },
+    { id: '3', title: 'Job 3', status: 'paused' },
+    { id: '4', title: 'Job 4', status: 'failed', error: 'Network error' }
+  ];
+  const groups = DownloadsPage.groupJobs(jobs);
+  assert.equal(groups.active.length, 1);
+  assert.equal(groups.queued.length, 1);
+  assert.equal(groups.paused.length, 1);
+  assert.equal(groups.failed.length, 1);
+  assert.equal(groups.active[0].id, '1');
+  assert.equal(groups.failed[0].error, 'Network error');
+});
+
+test('formatJobStatus produces plain text labels without emojis for all job states', () => {
+  assert.equal(DownloadsPage.formatJobStatus({ status: 'failed', error: 'Connection lost' }), 'Failed: Connection lost');
+  assert.equal(DownloadsPage.formatJobStatus({ status: 'failed' }), 'Save failed');
+  assert.equal(DownloadsPage.formatJobStatus({ status: 'paused' }), 'Paused — resume when you’re ready');
+  assert.equal(DownloadsPage.formatJobStatus({ status: 'queued' }), 'Waiting for a free slot…');
+  assert.equal(
+    DownloadsPage.formatJobStatus({ status: 'active', progress: { received: 10485760, total: 52428800 } }),
+    '10.0 / 50.0 MB'
+  );
+  assert.equal(
+    DownloadsPage.formatJobStatus({ status: 'active', progress: { phase: 'preparing', elapsed: 3000 } }),
+    'Preparing on server… 3 s'
+  );
+  assert.equal(DownloadsPage.formatJobStatus({ status: 'active', progress: { phase: 'verifying' } }), 'Verifying…');
+  assert.equal(DownloadsPage.formatJobStatus({ status: 'active' }), 'Saving for offline…');
+});
+
+test('bytes formatting handles bytes, MB, GB and invalid input safely', () => {
+  assert.equal(DownloadsPage.bytes(0), '0 MB');
+  assert.equal(DownloadsPage.bytes(10485760), '10.0 MB');
+  assert.equal(DownloadsPage.bytes(1073741824), '1.0 GB');
+  assert.equal(DownloadsPage.bytes(-100), '0 MB');
+  assert.equal(DownloadsPage.bytes(null), '0 MB');
+});
+
+test('escapeHtml escapes dangerous HTML characters', () => {
+  assert.equal(DownloadsPage.escapeHtml('<script>alert("xss")</script>'), '&lt;script&gt;alert(&quot;xss&quot;)&lt;/script&gt;');
+  assert.equal(DownloadsPage.escapeHtml('Tom & Jerry'), 'Tom &amp; Jerry');
+});
+