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/components/team/InvitationCard.vue

@@ -94,7 +94,7 @@ async function rejectInvitation() {
 
 .invitation-card:hover {
   border-color: var(--gg-primary);
-  box-shadow: 0 0 16px rgba(99, 102, 241, 0.12);
+  box-shadow: 0 0 16px rgba(5, 150, 105, 0.12);
 }
 
 .invitation-header {
@@ -211,6 +211,6 @@ async function rejectInvitation() {
 .reject-input textarea:focus {
   outline: none;
   border-color: var(--gg-primary);
-  box-shadow: 0 0 8px rgba(99, 102, 241, 0.15);
+  box-shadow: 0 0 8px rgba(5, 150, 105, 0.15);
 }
 </style>