feat: UI redesign v0.0.2 — color unification, navigation improvements, mobile support

- Unify color palette from mixed green/blue/purple to consistent green theme
- Sidebar: add text labels to create/join group buttons for discoverability
- Header: add quick action buttons (create group, join group, notifications)
- Mobile: add hamburger menu with slide-out sidebar and overlay
- Home: add prominent CTA buttons, onboarding card for empty state
- Join group dialog: add search-by-name mode alongside existing ID lookup
- Games library: inline group selector dropdown instead of external selection

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/views/Settings.vue

@@ -81,7 +81,7 @@ const showScheduleModal = ref(false)
 
 .setting-item:hover {
   border-color: var(--gg-primary);
-  box-shadow: 0 0 12px rgba(99, 102, 241, 0.1);
+  box-shadow: 0 0 12px rgba(5, 150, 105, 0.1);
 }
 
 .setting-info {
@@ -115,7 +115,7 @@ const showScheduleModal = ref(false)
 
 .setting-btn:hover:not(:disabled) {
   opacity: 0.9;
-  box-shadow: 0 0 12px rgba(99, 102, 241, 0.3);
+  box-shadow: 0 0 12px rgba(5, 150, 105, 0.3);
 }
 
 .setting-btn:disabled {