Fix RmlUi CSS compatibility issues in store, settings, and music apps

- Replace linear-gradient with solid colors (not supported in RmlUi)
- Replace border shorthand with border-width/border-color properties
- Replace display:grid with flexbox in music quick-access cards
- Remove unsupported transition property
- Fix border-radius: 50% to use 9999px in theme.rcss
- Fix third-party app icon/label sizes to match system apps (72x72px, 16px)
- Replace data-model bindings with static values in settings

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/main/assets/apps/home/home.rml

@@ -43,30 +43,31 @@
             width: 100%;
         }
 
+        /* Third-party apps use same sizing as system apps */
         #third-party-apps .app-icon {
             width: 25%;
             box-sizing: border-box;
         }
 
         #third-party-apps .app-icon-image {
-            width: 56px;
-            height: 56px;
-            border-radius: 14px;
+            width: 72px;
+            height: 72px;
+            border-radius: 18px;
             display: flex;
             align-items: center;
             justify-content: center;
-            margin: 0 auto 8px auto;
+            margin: 0 auto 12px auto;
             cursor: pointer;
         }
 
         #third-party-apps .app-icon-image:hover {
-            opacity: 0.8;
+            transform: scale(1.05);
         }
 
         #third-party-apps .app-icon-label {
             display: block;
             text-align: center;
-            font-size: 12px;
+            font-size: 16px;
             color: #FFFFFF;
         }
     </style>