feat: add settings option to hide Live TV categories (#11)

Add a liveChannelListMode setting (default 'grouped') with a Settings
toggle to display the Live TV channel list flat, without category
group sections. When enabled, logical channels are listed directly
with their stream variants still grouped as in #9/#10. Cover the
setting default and flat-list behavior with tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

test/channelVariantGrouping.test.js

@@ -42,3 +42,20 @@ test('an explicit visible selection overrides the automatic quality preference',
     const logical = grouping.groupChannels([hd, uhd], { selectedVariants })[0];
     assert.equal(logical.preferredVariant.id, '1');
 });
+
+test('flat list ordering promotes favorites without duplicating channels', () => {
+    const channels = [
+        { id: 'one', isFavorite: false },
+        { id: 'two', isFavorite: true },
+        { id: 'three', isFavorite: false },
+        { id: 'four', isFavorite: true }
+    ];
+    const ordered = grouping.orderFlatChannels(channels);
+    assert.deepEqual(ordered.map(item => item.id), ['two', 'four', 'one', 'three']);
+    assert.equal(new Set(ordered.map(item => item.id)).size, channels.length);
+});
+
+test('favorites group updates are disabled for flat lists', () => {
+    assert.equal(grouping.shouldUseFavoritesGroup('flat'), false);
+    assert.equal(grouping.shouldUseFavoritesGroup('grouped'), true);
+});

test/settingsDefaults.test.js

@@ -0,0 +1,7 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const { getDefaultSettings } = require('../server/db');
+
+test('defaults Live TV channel lists to grouped mode', () => {
+    assert.equal(getDefaultSettings().liveChannelListMode, 'grouped');
+});