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>

index.html

@@ -4,6 +4,12 @@
     <meta charset="UTF-8" />
     <link rel="icon" type="image/svg+xml" href="/vite.svg" />
     <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <link rel="preconnect" href="https://fonts.googleapis.com" />
+    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
+    <link
+      href="https://fonts.googleapis.com/css2?family=Cinzel:wght@700&family=Nunito:wght@400;700;800;900&family=Nunito+Sans:wght@400;600;700&family=Sorts+Mill+Goudy:ital@0;1&display=swap"
+      rel="stylesheet"
+    />
     <script src="https://www.geogebra.org/apps/deployggb.js"></script>
 
     <script