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/css/styles.css

@@ -1214,8 +1214,8 @@
 
 .view-toggle-btn:hover {
     color: var(--text-primary);
-    background: var(--border);
-    transform: none;
+    background: transparent !important;
+    transform: none !important;
 }
 
 .view-toggle-btn.active {
@@ -1223,6 +1223,10 @@
     background: var(--bg-primary);
 }
 
+.browser-refresh-btn {
+    margin-left: 0.35rem;
+}
+
 .view-toggle-btn svg {
     fill: currentColor;
 }