fix: resolve bugs and improve frontend performance

- Fix register not resetting isLoading on success (causing login page to hang)
- Fix leaderboard streaks 400 error by forcing all_time timeframe
- Reorder routes so static paths match before dynamic practice/:sheetId
- Lazy-load QuestMap + Three.js (saves ~350KB gzip on initial load)
- Move KaTeX CSS to lazy import (only loads on math pages)
- Remove 28 duplicate Google Font @import lines from component CSS
- Add font preconnect + single stylesheet link in index.html
- Replace 8 unsafe JSON.parse(localStorage) calls with Zustand selectors
- Add global ErrorBoundary to prevent full-app crashes
- Extract arcTheme utilities to break static import cycle with QuestMap
- Merge Three.js + Troika into single chunk to fix circular dependency

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

vite.config.ts

@@ -15,7 +15,13 @@ export default defineConfig({
     rollupOptions: {
       output: {
         manualChunks: {
-          troika: ["troika-three-text", "troika-worker-utils"],
+          three: [
+            "three",
+            "@react-three/fiber",
+            "@react-three/drei",
+            "troika-three-text",
+            "troika-worker-utils",
+          ],
         },
       },
     },