Init commit from initial prompt

src/lib/checklist.ts

@@ -0,0 +1,22 @@
+export const CHECKLIST_KEY = 'magikarp-checklist-v1';
+
+export function loadChecklist(): Set<string> {
+  if (typeof window === 'undefined') return new Set();
+  try {
+    const raw = localStorage.getItem(CHECKLIST_KEY);
+    if (!raw) return new Set();
+    const arr = JSON.parse(raw) as string[];
+    return new Set(arr);
+  } catch {
+    return new Set();
+  }
+}
+
+export function saveChecklist(set: Set<string>) {
+  if (typeof window === 'undefined') return;
+  try {
+    localStorage.setItem(CHECKLIST_KEY, JSON.stringify(Array.from(set)));
+  } catch {
+    // ignore
+  }
+}