Add UX enhancements: carousel, filter chips, command palette, and more

- Replace featured section Stack with AdwCarousel + indicator dots
- Convert category grid to horizontal scrollable filter chips
- Add grid/list view toggle for catalog with compact row layout
- Add quick launch button on library list rows
- Add stale catalog banner when data is older than 7 days
- Add command palette (Ctrl+K) for quick app search and launch
- Show specific app names in update notifications
- Add per-app auto-update toggle (skip updates switch)
- Add keyboard shortcut hints to button tooltips
- Add source trust badges (AppImageHub/Community) on catalog tiles
- Add undo-based uninstall with toast and record restoration
- Add type-to-search in library view
- Use human-readable catalog source labels
- Show Launch button for installed apps in catalog detail
- Replace external browser link with inline AppImage explainer dialog

data/resources/style.css

@@ -364,3 +364,28 @@ window.lightbox .lightbox-nav {
 .stat-card image {
     opacity: 0.55;
 }
+
+/* ===== Catalog Row (compact list view) ===== */
+.catalog-row {
+    border: 1px solid alpha(@window_fg_color, 0.08);
+    border-radius: 8px;
+    padding: 0;
+}
+
+.catalog-row:hover {
+    border-color: alpha(@accent_bg_color, 0.4);
+}
+
+/* ===== Skeleton Loading Placeholder ===== */
+.skeleton-card {
+    background: alpha(@card_bg_color, 0.5);
+    border-radius: 12px;
+    min-height: 180px;
+    min-width: 140px;
+    animation: skeleton-pulse 1.5s ease-in-out infinite;
+}
+
+@keyframes skeleton-pulse {
+    0%, 100% { opacity: 0.4; }
+    50% { opacity: 0.7; }
+}