feat(app): add error/loading boundaries and update dashboard routes

- Add error.tsx and loading.tsx boundaries for admin, parent, student, teacher routes

- Add dashboard-error-fallback and dashboard-loading-skeleton components

- Add student/learning page, parent/leave routes, teacher textbook components

- Update existing app routes across auth, dashboard, and API endpoints

- Update proxy middleware and next-auth type declarations

src/modules/dashboard/components/teacher-dashboard/teacher-grade-trends.tsx

@@ -59,7 +59,7 @@ export function TeacherGradeTrends({ trends }: { trends: TeacherGradeTrendItem[]
             .reverse()
             .slice(0, 3)
             .map((item, i) => (
-              <div key={i} className="flex flex-col gap-1 rounded-lg border p-3 bg-card/50">
+              <div key={item.fullTitle || `item-${i}`} className="flex flex-col gap-1 rounded-lg border p-3 bg-card/50">
                 <div className="text-xs text-muted-foreground truncate" title={item.fullTitle}>
                   {item.fullTitle}
                 </div>