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

server.js

@@ -0,0 +1,52 @@
+import express from 'express';
+import path from 'path';
+import { fileURLToPath } from 'url';
+import fs from 'fs/promises';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+
+export function startServer() {
+    const app = express();
+    const PORT = process.env.SERVER_PORT || 3000;
+    const HOST = process.env.SERVER_HOST || '0.0.0.0';
+    const CACHE_DIR = process.env.CACHE_LOCATION || './cache';
+
+    // Serve category tree JSON
+    app.get('/api/categories', async (req, res) => {
+        try {
+            const treePath = path.join(CACHE_DIR, 'category_tree.json');
+            const data = await fs.readFile(treePath, 'utf-8');
+            res.json(JSON.parse(data));
+        } catch (err) {
+            res.status(500).json({ error: 'Failed to load category tree' });
+        }
+    });
+
+    // Serve category images
+    app.get('/img/cat/:id.avif', (req, res) => {
+        const { id } = req.params;
+        const imagePath = path.join(CACHE_DIR, 'img', 'categories', `${id}.avif`);
+        res.sendFile(path.resolve(imagePath), (err) => {
+            if (err) {
+                res.status(404).send('Image not found');
+            }
+        });
+    });
+
+    // Serve index.html
+    app.get('/', (req, res) => {
+        const htmlPath = path.join(__dirname, 'index.html');
+        console.log('Attempting to serve:', htmlPath);
+        res.sendFile(htmlPath, (err) => {
+            if (err) {
+                console.error('Error serving index.html:', err);
+                res.status(500).send('Error loading page');
+            }
+        });
+    });
+
+    app.listen(PORT, HOST, () => {
+        console.log(`🌐 Server running on http://${HOST}:${PORT}`);
+    });
+}