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/utils/cache.js

@@ -36,13 +36,17 @@ class MemoryCache {
     let totalSize = 0;
 
     for (const [key, entry] of this.store.entries()) {
-      const json = JSON.stringify(entry.value);
+      // Maps must be converted before JSON.stringify (which renders them as "{}")
+      const serializable = entry.value instanceof Map ? Object.fromEntries(entry.value) : entry.value;
+      const json = JSON.stringify(serializable);
       const sizeBytes = Buffer.byteLength(json, 'utf8');
       totalSize += sizeBytes;
       const ttlRemaining = Math.max(0, entry.expiresAt - now);
       const expired = now > entry.expiresAt;
       let itemCount = null;
-      if (Array.isArray(entry.value)) {
+      if (entry.value instanceof Map) {
+        itemCount = entry.value.size;
+      } else if (Array.isArray(entry.value)) {
         itemCount = entry.value.length;
       } else if (entry.value && typeof entry.value === 'object') {
         if (Array.isArray(entry.value.records)) itemCount = entry.value.records.length;