Add coverImage poster to player, fix TipTap v3 editor reset, quiz admin preview

- Add coverImage field to Lesson model (prisma)
- Pass coverImage as poster prop to KinescopePlayer
- Show quiz in read-only preview mode for admin on lesson page
- Fix TipTap v3 editor reset on save: pass [lesson.id] as deps to useEditor
  to prevent setOptions() from reinitializing content on every re-render
- Replace saveLesson Server Action call with fetch PATCH /api/admin/lessons/[id]
  to avoid Next.js 16 automatic RSC refresh after Server Actions
- Simplify revalidatePath: only revalidate module page, not lesson editor page

src/components/admin/lesson-editor.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { useState, useCallback, useTransition } from "react";
+import { useState, useCallback } from "react";
 import { useEditor, EditorContent } from "@tiptap/react";
 import StarterKit from "@tiptap/starter-kit";
 import Image from "@tiptap/extension-image";
@@ -9,7 +9,6 @@ import Underline from "@tiptap/extension-underline";
 import Placeholder from "@tiptap/extension-placeholder";
 import { Save, Eye, FileUp, ChevronLeft, ChevronRight } from "lucide-react";
 import { useRouter } from "next/navigation";
-import { saveLesson } from "@/lib/actions/lesson-actions";
 
 interface LessonData {
   id: string;
@@ -47,7 +46,8 @@ export function LessonEditor({
   const [importing, setImporting] = useState(false);
   const [importError, setImportError] = useState<string | null>(null);
   const [saved, setSaved] = useState(false);
-  const [pending, startTransition] = useTransition();
+  const [saveError, setSaveError] = useState<string | null>(null);
+  const [pending, setPending] = useState(false);
 
   const inputStyle = {
     border: "2px solid var(--border)",
@@ -73,7 +73,7 @@ export function LessonEditor({
         class: "prose prose-slate max-w-none min-h-[300px] focus:outline-none p-4",
       },
     },
-  });
+  }, [lesson.id]);
 
   const uploadImage = useCallback(async () => {
     const input = document.createElement("input");
@@ -133,18 +133,27 @@ export function LessonEditor({
     }
   }, [editor]);
 
-  function handleSave() {
+  async function handleSave() {
     if (!editor) return;
-    startTransition(async () => {
-      await saveLesson(lesson.id, courseId, moduleId, {
-        title,
-        kinescopeId,
-        content: editor.getJSON(),
-        published,
+    setPending(true);
+    setSaveError(null);
+    try {
+      const res = await fetch(`/api/admin/lessons/${lesson.id}`, {
+        method: "PATCH",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ title, kinescopeId, content: editor.getJSON(), published }),
       });
+      if (!res.ok) {
+        const data = await res.json().catch(() => ({}));
+        throw new Error((data as { error?: string }).error ?? `HTTP ${res.status}`);
+      }
       setSaved(true);
       setTimeout(() => setSaved(false), 2000);
-    });
+    } catch (err) {
+      setSaveError(err instanceof Error ? err.message : "Ошибка сохранения");
+    } finally {
+      setPending(false);
+    }
   }
 
   function navigateTo(lessonId: string) {
@@ -266,6 +275,12 @@ export function LessonEditor({
         </p>
       )}
 
+      {saveError && (
+        <p className="text-xs px-3 py-2" style={{ background: "oklch(0.577 0.245 27.325 / 0.1)", color: "oklch(0.577 0.245 27.325)", border: "1px solid oklch(0.577 0.245 27.325 / 0.3)" }}>
+          Ошибка сохранения: {saveError}
+        </p>
+      )}
+
       {/* Title */}
       <div className="space-y-1">
         <label className="text-xs font-bold uppercase tracking-widest" style={{ color: "var(--muted-foreground)" }}>