✨ feat(manacore): add gift code web UI

Add web interface for redeeming and managing gift codes:
- API service for all gift operations (create, redeem, list, cancel)
- Public preview page at /g/[code] for gift info before login
- Protected redemption flow with riddle support
- Dashboard with tabs: received gifts, created codes, create new
- Gift icon added to navigation and shared-ui

packages/shared-ui/src/navigation/PillNavigation.svelte

@@ -59,6 +59,7 @@
 		Robot,
 		Key,
 		Shield,
+		Gift,
 	} from '@manacore/shared-icons';
 
 	// Map icon names to Phosphor components
@@ -113,6 +114,7 @@
 		robot: Robot,
 		key: Key,
 		shield: Shield,
+		gift: Gift,
 	};
 
 	// Convert app items to dropdown items (will be computed as derived)