Add in-content video embed and image replace/delete controls

- KinescopeVideo TipTap node: insert video anywhere in lesson content via toolbar button; editor shows ID preview, student view renders KinescopePlayer
- ImageWithControls NodeView: hover over any image in editor to reveal Replace and Delete buttons

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/student/lesson-content.tsx

@@ -1,16 +1,56 @@
 "use client";
 
-import { useEditor, EditorContent } from "@tiptap/react";
+import { useEditor, EditorContent, NodeViewWrapper, ReactNodeViewRenderer } from "@tiptap/react";
+import { Node, mergeAttributes } from "@tiptap/core";
 import StarterKit from "@tiptap/starter-kit";
 import Image from "@tiptap/extension-image";
 import Link from "@tiptap/extension-link";
+import Underline from "@tiptap/extension-underline";
+import { KinescopePlayer } from "@/components/player/kinescope-player";
+
+function KinescopeVideoStudentView({ node }: { node: { attrs: Record<string, unknown> } }) {
+  const videoId = node.attrs.videoId as string;
+  if (!videoId) return null;
+  return (
+    <NodeViewWrapper>
+      <div className="my-6">
+        <KinescopePlayer videoId={videoId} />
+      </div>
+    </NodeViewWrapper>
+  );
+}
+
+const KinescopeVideoExtension = Node.create({
+  name: "kinescopeVideo",
+  group: "block",
+  atom: true,
+
+  addAttributes() {
+    return { videoId: { default: "" } };
+  },
+
+  parseHTML() {
+    return [{ tag: "div[data-kinescope-video]" }];
+  },
+
+  renderHTML({ HTMLAttributes }) {
+    return ["div", mergeAttributes({ "data-kinescope-video": "" }, HTMLAttributes)];
+  },
+
+  addNodeView() {
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    return ReactNodeViewRenderer(KinescopeVideoStudentView as any);
+  },
+});
 
 export function LessonContent({ content }: { content: object }) {
   const editor = useEditor({
     extensions: [
       StarterKit,
+      Underline,
       Image.configure({ inline: false }),
       Link.configure({ openOnClick: true }),
+      KinescopeVideoExtension,
     ],
     content,
     editable: false,