UI polish: refresh button, negative thumbnail cache, and style fixes

- Add refresh button to browser toolbar to re-fetch current folder
- Cache "no thumbnail" results to avoid repeated slow SMB lookups
- Fix list view fallback icon sizing for files without album art
- Fix view toggle button hover (no background/scale on hover)
- Skip re-render when clicking already-active view mode button

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

media_server/static/js/app.js

@@ -1873,11 +1873,16 @@ async function loadThumbnail(imgElement, fileName) {
         } else {
             // Fallback to icon (204 = no thumbnail available)
             const parent = imgElement.parentElement;
+            const isList = parent.classList.contains('browser-list-icon');
             imgElement.remove();
-            const icon = document.createElement('div');
-            icon.className = 'browser-icon';
-            icon.textContent = '🎵';
-            parent.insertBefore(icon, parent.firstChild);
+            if (isList) {
+                parent.textContent = '🎵';
+            } else {
+                const icon = document.createElement('div');
+                icon.className = 'browser-icon';
+                icon.textContent = '🎵';
+                parent.insertBefore(icon, parent.firstChild);
+            }
         }
     } catch (error) {
         console.error('Error loading thumbnail:', error);
@@ -2008,7 +2013,16 @@ function nextPage() {
     }
 }
 
+function refreshBrowser() {
+    if (currentFolderId) {
+        browsePath(currentFolderId, currentPath, currentOffset);
+    } else {
+        loadMediaFolders();
+    }
+}
+
 function setViewMode(mode) {
+    if (mode === viewMode) return;
     viewMode = mode;
     localStorage.setItem('mediaBrowser.viewMode', mode);