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>

public/js/services/channelVariantGrouping.js

@@ -152,11 +152,24 @@
         }).filter(channel => showHidden || !channel.isHidden);
     }
 
+    function orderFlatChannels(channels) {
+        return channels.map((channel, index) => ({ channel, index })).sort((a, b) => {
+            const favoriteDifference = Number(b.channel.isFavorite) - Number(a.channel.isFavorite);
+            return favoriteDifference || a.index - b.index;
+        }).map(entry => entry.channel);
+    }
+
+    function shouldUseFavoritesGroup(listMode) {
+        return listMode === 'grouped';
+    }
+
     return {
         normalizeChannelName,
         displayNameForFingerprint,
         getVariantKey,
         getQuality,
-        groupChannels
+        groupChannels,
+        orderFlatChannels,
+        shouldUseFavoritesGroup
     };
 });