fix(web): pass full ProseMirror doc to editor, not bare array

WritingView passed chapter.doc.content (a bare ProseMirror node array)
as the editor content, which made EditorState.create build a doc node
with an undefined type, throwing 'Cannot read properties of undefined
(reading schema)' and unmounting the write view. Pass the full doc
object ({ type: 'doc', content }) on init and on setContent sync.

Add editor regression tests covering schema instantiation, node
registration, and doc-content round-trip.

packages/editor/src/use-editor-doc.test.ts

@@ -0,0 +1,26 @@
+import { describe, it, expect } from "vitest";
+import { createPubScriptEditor } from "./schema.js";
+
+/** Minimal full ProseMirror doc, mirroring a seeded chapter.doc. */
+const fullDoc = {
+  type: "doc",
+  content: [
+    { type: "heading", attrs: { level: 1 }, content: [{ type: "text", text: "The Glass Harbor" }] },
+    { type: "paragraph", content: [{ type: "text", text: "Salt hung in the air." }] },
+  ],
+};
+
+/** Bare array — the exact bug that crashed EditorState.create in the browser. */
+const bareArray = fullDoc.content;
+
+describe("editor content parsing (regression: bare array vs full doc)", () => {
+  it("builds an editor from a full doc object (the seeded chapter.doc shape)", () => {
+    const editor = createPubScriptEditor({ content: fullDoc });
+    expect(editor).not.toBeNull();
+    expect(editor.state.doc.type.name).toBe("doc");
+  });
+
+  it("throws on a bare content array (documents the regression we fixed)", () => {
+    expect(() => createPubScriptEditor({ content: bareArray })).toThrow();
+  });
+});