feat(editor): add TipTap semantic editor

src/editor/extensions.ts

@@ -0,0 +1,11 @@
+import type { Extensions } from "@tiptap/core";
+import StarterKit from "@tiptap/starter-kit";
+import Placeholder from "@tiptap/extension-placeholder";
+
+export const editorExtensions: Extensions = [
+  StarterKit.configure({
+    heading: { levels: [2, 3] },
+    codeBlock: false,
+  }),
+  Placeholder.configure({ placeholder: "Begin your chapter…" }),
+];