Add cache-busting query strings and no-cache for HTML files

Proxy was caching old admin.js; ?v=3 query string forces a fresh fetch.
Also extend no-cache header to .html files so future deploys propagate immediately.

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

server.js

@@ -36,7 +36,7 @@ const app = express();
 app.use(express.json({ limit: '15mb' })); // photos for page-scanning are base64 in the JSON body
 app.use(express.static(join(ROOT, 'public'), {
   setHeaders(res, filePath) {
-    if (filePath.endsWith('.css') || filePath.endsWith('.js')) {
+    if (filePath.endsWith('.css') || filePath.endsWith('.js') || filePath.endsWith('.html')) {
       res.setHeader('Cache-Control', 'no-cache');
     }
   },