Add modern UI enhancements over the classic redesign

Layered progressive polish on the warm classic + brass theme:
- Card entrance animation on first mount (virtualizer-aware)
- Cursor-tracking brass spotlight border on cards
- Thumbnail skeleton shimmer until the poster paints
- Hover video preview after a short dwell (only when formats resolved)
- View Transition + blurred-poster ambient backdrop on player open
- Favorite heart pop + expanding ring on add
- ⌘K command palette (search, theme, density, reels, source/channel)
- Scroll-progress bar + back-to-top FAB
- Grid density toggle (comfortable/compact)
- Reels HUD: serif title, brass scrubber, muted-state pulse

All new motion respects prefers-reduced-motion; no JS/HTML structure
changes to the core grid/feed. New glue lives in frontend/js/enhance.js.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/js/storage.js

@@ -48,6 +48,15 @@ App.session = App.session || {};
         localStorage.setItem(FEED_END_BEHAVIOR_KEY, nextBehavior === 'scroll' ? 'scroll' : 'loop');
     };
 
+    // Grid density: 'comfortable' (default) or 'compact' (more, smaller columns).
+    App.storage.getDensity = function() {
+        return localStorage.getItem('density') === 'compact' ? 'compact' : 'comfortable';
+    };
+
+    App.storage.setDensity = function(nextDensity) {
+        localStorage.setItem('density', nextDensity === 'compact' ? 'compact' : 'comfortable');
+    };
+
     App.storage.getServerEntries = function() {
         const config = App.storage.getConfig();
         if (!config.servers || !Array.isArray(config.servers)) return [];