feat(editor): add figure block with placement and caption

src/editor/extensions.ts

@@ -1,11 +1,15 @@
 import type { Extensions } from "@tiptap/core";
 import StarterKit from "@tiptap/starter-kit";
 import Placeholder from "@tiptap/extension-placeholder";
+import { Figure } from "./figure";
 
 export const editorExtensions: Extensions = [
   StarterKit.configure({
     heading: { levels: [2, 3] },
     codeBlock: false,
   }),
-  Placeholder.configure({ placeholder: "Begin your chapter…" }),
+  Placeholder.configure({
+    placeholder: ({ node }) => (node.type.name === "heading" ? "" : "Begin your chapter…"),
+  }),
+  Figure,
 ];