feat: Node.js server + editor save/load + keyboard controls

- Replace nginx with Node.js server that serves static files AND
  provides API endpoints for reading/writing maps.js directly
  (GET/PUT /api/maps). Creates .bak backup before each save.
- Editor: arrow keys to pan, +/- to zoom, Ctrl+S to save
- Editor: "Save" button writes maps.js directly on the server
- Editor: "Load" button reads and parses maps.js from server
- Editor: auto-loads from server on page open
- Dockerfile changed from nginx:alpine to node:20-alpine

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server.js

@@ -0,0 +1,131 @@
+// Lightweight static file server + editor API for saving maps.js
+// Used in production Docker container
+
+const http = require('http');
+const fs = require('fs');
+const path = require('path');
+
+const PORT = process.env.PORT || 80;
+const STATIC_DIR = path.join(__dirname, 'public');
+const MAPS_FILE = path.join(STATIC_DIR, 'js', 'world', 'maps.js');
+
+const MIME = {
+    '.html': 'text/html',
+    '.css': 'text/css',
+    '.js': 'application/javascript',
+    '.json': 'application/json',
+    '.png': 'image/png',
+    '.jpg': 'image/jpeg',
+    '.svg': 'image/svg+xml',
+    '.ico': 'image/x-icon',
+    '.woff2': 'font/woff2',
+};
+
+const server = http.createServer((req, res) => {
+    // CORS headers for editor
+    res.setHeader('Access-Control-Allow-Origin', '*');
+    res.setHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, OPTIONS');
+    res.setHeader('Access-Control-Allow-Headers', 'Content-Type');
+
+    if (req.method === 'OPTIONS') {
+        res.writeHead(204);
+        res.end();
+        return;
+    }
+
+    // === API: GET /api/maps — read maps.js source ===
+    if (req.method === 'GET' && req.url === '/api/maps') {
+        fs.readFile(MAPS_FILE, 'utf-8', (err, data) => {
+            if (err) {
+                res.writeHead(500, { 'Content-Type': 'application/json' });
+                res.end(JSON.stringify({ error: 'Failed to read maps.js' }));
+                return;
+            }
+            res.writeHead(200, { 'Content-Type': 'application/json' });
+            res.end(JSON.stringify({ content: data }));
+        });
+        return;
+    }
+
+    // === API: PUT /api/maps — write maps.js source ===
+    if (req.method === 'PUT' && req.url === '/api/maps') {
+        let body = '';
+        req.on('data', chunk => { body += chunk; });
+        req.on('end', () => {
+            try {
+                const { content } = JSON.parse(body);
+                if (!content || typeof content !== 'string') {
+                    res.writeHead(400, { 'Content-Type': 'application/json' });
+                    res.end(JSON.stringify({ error: 'Missing content field' }));
+                    return;
+                }
+                // Backup before overwrite
+                const backup = MAPS_FILE + '.bak';
+                if (fs.existsSync(MAPS_FILE)) {
+                    fs.copyFileSync(MAPS_FILE, backup);
+                }
+                fs.writeFileSync(MAPS_FILE, content, 'utf-8');
+                console.log(`[server] maps.js saved (${content.length} bytes)`);
+                res.writeHead(200, { 'Content-Type': 'application/json' });
+                res.end(JSON.stringify({ ok: true, bytes: content.length }));
+            } catch (e) {
+                res.writeHead(400, { 'Content-Type': 'application/json' });
+                res.end(JSON.stringify({ error: e.message }));
+            }
+        });
+        return;
+    }
+
+    // === API: GET /api/maps/json — parse current map data as JSON ===
+    if (req.method === 'GET' && req.url === '/api/maps/json') {
+        fs.readFile(MAPS_FILE, 'utf-8', (err, data) => {
+            if (err) {
+                res.writeHead(500, { 'Content-Type': 'application/json' });
+                res.end(JSON.stringify({ error: 'Failed to read maps.js' }));
+                return;
+            }
+            // Extract JSON-serializable data from the JS source
+            // This is a best-effort parser for the generated maps.js format
+            res.writeHead(200, { 'Content-Type': 'application/json' });
+            res.end(JSON.stringify({ source: data }));
+        });
+        return;
+    }
+
+    // === Static file serving ===
+    let filePath = path.join(STATIC_DIR, req.url === '/' ? 'index.html' : req.url);
+    // Prevent directory traversal
+    if (!filePath.startsWith(STATIC_DIR)) {
+        res.writeHead(403);
+        res.end('Forbidden');
+        return;
+    }
+
+    const ext = path.extname(filePath).toLowerCase();
+    const contentType = MIME[ext] || 'application/octet-stream';
+
+    fs.readFile(filePath, (err, data) => {
+        if (err) {
+            if (err.code === 'ENOENT') {
+                res.writeHead(404);
+                res.end('Not found');
+            } else {
+                res.writeHead(500);
+                res.end('Server error');
+            }
+            return;
+        }
+        // Cache static assets
+        if (ext === '.png' || ext === '.jpg' || ext === '.woff2') {
+            res.setHeader('Cache-Control', 'public, max-age=86400');
+        }
+        res.writeHead(200, { 'Content-Type': contentType });
+        res.end(data);
+    });
+});
+
+server.listen(PORT, () => {
+    console.log(`[server] Logic Gates running on port ${PORT}`);
+    console.log(`[server] Static: ${STATIC_DIR}`);
+    console.log(`[server] Maps file: ${MAPS_FILE}`);
+});