feat(frontend): lessons page with filter (replaces Admin.tsx)

packages/frontend/src/pages/Lessons.tsx

@@ -0,0 +1,61 @@
+import { useEffect, useState } from 'react';
+import { lessonsApi } from '../api/lessons.js';
+import { useLessons } from '../stores/lessonsStore.js';
+import { LessonTree } from '../components/LessonTree.js';
+
+export function LessonsPage() {
+  const { tree, refresh, loading } = useLessons();
+  const [newRoot, setNewRoot] = useState('');
+  const [filter, setFilter] = useState('');
+
+  useEffect(() => { refresh(); }, [refresh]);
+
+  async function addRoot() {
+    if (!newRoot.trim()) return;
+    await lessonsApi.create({ name: newRoot.trim(), parentId: null });
+    setNewRoot('');
+    await refresh();
+  }
+
+  return (
+    <div className="mx-auto max-w-3xl space-y-6">
+      <header>
+        <h1 className="font-display text-3xl font-bold">Lessen</h1>
+        <p className="mt-1 text-sm text-slate-600 dark:text-slate-400">
+          Maak een hiërarchie van lessen en sublessen. Sleep aan ⋮⋮ om te herordenen. Klik op een les voor details.
+        </p>
+      </header>
+
+      <div className="surface flex flex-col gap-2 p-4 sm:flex-row">
+        <input
+          className="input-field"
+          placeholder="Nieuwe wortel-les…"
+          value={newRoot}
+          onChange={(e) => setNewRoot(e.target.value)}
+          onKeyDown={(e) => e.key === 'Enter' && addRoot()}
+        />
+        <button className="btn-primary shrink-0" onClick={addRoot} disabled={!newRoot.trim()}>
+          + Toevoegen
+        </button>
+      </div>
+
+      <div className="surface space-y-3 p-4">
+        <input
+          className="input-field"
+          placeholder="Filter lessen op naam…"
+          value={filter}
+          onChange={(e) => setFilter(e.target.value)}
+        />
+        {loading ? (
+          <p className="text-sm text-slate-500">Laden…</p>
+        ) : tree.length === 0 ? (
+          <div className="py-8 text-center text-sm text-slate-500">
+            Nog geen lessen. Voeg er hierboven een toe.
+          </div>
+        ) : (
+          <LessonTree nodes={tree} filter={filter} />
+        )}
+      </div>
+    </div>
+  );
+}