frontend: refactor build viewer a bit more

frontend/utils/mockData.ts

@@ -0,0 +1,16 @@
+/**
+ * Mock data for development and fallback scenarios
+ * Used when API data is not available
+ */
+
+export const MOCK_SUMMONER_SPELLS = [
+  { id: 4, count: 1000, pickrate: 0.45 }, // Flash
+  { id: 7, count: 800, pickrate: 0.35 }, // Heal
+  { id: 14, count: 600, pickrate: 0.15 }, // Ignite
+  { id: 3, count: 200, pickrate: 0.05 } // Exhaust
+]
+
+/**
+ * Constants used throughout the application
+ */
+export const BOOTS_RUSH_THRESHOLD = 0.5