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>

src/pages/student/practice-sheet/page.tsx

@@ -17,6 +17,7 @@ import {
 import { useNavigate } from "react-router-dom";
 import { api } from "../../../utils/api";
 import { type PracticeSheet } from "../../../types/sheet";
+import { useAuthStore } from "../../../stores/authStore";
 
 /* ─────────────────────────────────────────────
    Ambient decoration
@@ -415,7 +416,6 @@ const EmptyState = ({ query }: { query: string }) => (
    Styles
 ───────────────────────────────────────────── */
 const STYLES = `
-  @import url('https://fonts.googleapis.com/css2?family=Nunito:wght@400;700;800;900&family=Nunito+Sans:wght@400;600;700&display=swap');
 
   :root { --content-max: 1100px; }
 
@@ -700,6 +700,7 @@ type ViewMode = "standard" | "compact";
 
 export const PracticeSheetList = () => {
   const navigate = useNavigate();
+  const token = useAuthStore((state) => state.token);
   const [sheets, setSheets] = useState<PracticeSheet[]>([]);
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState<string | null>(null);
@@ -707,13 +708,8 @@ export const PracticeSheetList = () => {
   const [viewMode, setViewMode] = useState<ViewMode>("compact");
 
   useEffect(() => {
-    setLoading(true);
-    const authStorage = localStorage.getItem("auth-storage");
-    if (!authStorage) return;
-    const {
-      state: { token },
-    } = JSON.parse(authStorage);
     if (!token) return;
+    setLoading(true);
     api
       .getPracticeSheets(token, 1, 10)
       .then((data) => {