feat: Add web server and UI for category tree display, and update picture syncer to use AVIF format.

index.js

@@ -1,5 +1,6 @@
 import categorySyncer from './category-syncer.js';
 import pictureSyncer from './picture-syncer.js';
+import { startServer } from './server.js';
 
 categorySyncer.on('synced', async ({ tree, unprunedTree, changed }) => {
     if (changed) {
@@ -44,3 +45,6 @@ if (process.stdout.isTTY) {
         process.exit(0);
     });
 }
+
+// Start Express server
+startServer();