Tighten typing and input validation across study pages

src/app/(protected)/[classSlug]/flashcards/page.tsx

@@ -27,6 +27,7 @@ import {
   useSortable,
 } from "@dnd-kit/sortable";
 import { CSS } from "@dnd-kit/utilities";
+import type { ReorderItem } from "@/types/study";
 
 interface DeckItem {
   id: string;
@@ -65,7 +66,14 @@ function getProgressLabel(deck: DeckItem) {
   return `${current}/${total}, ${modeLabel} · ${correctCount} ✓`;
 }
 
-function SortableDeckCard({ deck, onEdit, onDelete, classSlug }: any) {
+interface SortableDeckCardProps {
+  deck: DeckItem;
+  onEdit: (deck: DeckItem) => void;
+  onDelete: (deck: DeckItem) => void;
+  classSlug: string;
+}
+
+function SortableDeckCard({ deck, onEdit, onDelete, classSlug }: SortableDeckCardProps) {
   const { attributes, listeners, setNodeRef, transform, transition, isDragging } = useSortable({ id: deck.id });
   const style = {
     transform: CSS.Transform.toString(transform),
@@ -314,8 +322,6 @@ export default function FlashcardsPage() {
     if (!activeDeck) return;
 
     let targetGroupId: string | null = null;
-    let targetIndex = 0;
-
     const overContainerId = over.data.current?.sortable?.containerId;
     if (overContainerId) {
        targetGroupId = overContainerId === "uncategorized" ? null : overContainerId;
@@ -344,7 +350,7 @@ export default function FlashcardsPage() {
         }
 
         const affectedGroups = new Set([activeDeck.groupId, targetGroupId]);
-        const updates: any[] = [];
+        const updates: ReorderItem[] = [];
         
         affectedGroups.forEach(gId => {
            const gItems = newItems.filter(d => d.groupId === gId);