fix: correct status panel cache stats and static asset caching

cache.js: Map values serialise as '{}' under JSON.stringify, causing
emby:users to show 0 bytes and null item count in the status panel.
Convert Maps via Object.fromEntries before stringifying, and report
Map.size as itemCount.

index.js: JS and CSS served with Cache-Control: no-cache so browsers
always revalidate on load. ETag still prevents re-downloading unchanged
files — only a new deploy triggers an actual download.

server/index.js

@@ -202,8 +202,17 @@ app.get('/ready', (req, res) => {
 const PUBLIC_DIR = path.join(__dirname, '../public');
 const INDEX_HTML = path.join(PUBLIC_DIR, 'index.html');
 
-// Serve all static assets (js, css, images, icons) except index.html
-app.use(express.static(PUBLIC_DIR, { index: false }));
+// Serve all static assets (js, css, images, icons) except index.html.
+// JS and CSS get no-cache so browsers revalidate on every load (ETag still
+// avoids re-downloading unchanged files; only a deploy changes the ETag).
+app.use(express.static(PUBLIC_DIR, {
+  index: false,
+  setHeaders(res, filePath) {
+    if (filePath.endsWith('.js') || filePath.endsWith('.css')) {
+      res.setHeader('Cache-Control', 'no-cache');
+    }
+  }
+}));
 
 // Serve index.html with nonce injected into the <script> and <link> tags
 function serveIndex(req, res) {