Add on-page editor for the go-graph-cms

Injectable React editor that is side-loaded onto the statically rendered
page and edits through the CMS HTTP API (POST /api/edit).

- Shadow-root UI over server HTML; patches morphed in, undo/redo from
  server inverses (reuses @k6n/cms-editor EditClient/morph/markdown editor)
- Sign-in via go-auth device grant as the CMS client (aud matches), token
  refresh + 401 retry; live preview swapped in on load and on tab focus
- Schema-driven property form (arrays, maps, variants, $ref, validation)
- Every string property editable where it is rendered (value-bound inline
  fields and attribute chips), markdown WYSIWYG for marked fields
- Block palette + drag & drop with ghost drop targets, insertion slots,
  sort snapping between siblings (Alt to nest)
- x-style annotations: on-page padding/margin/gap handles, Style panel,
  wrap-in-layout; x-graph label/group for titles and grouping
- Dev workflow: Vite proxy to the live site (token injected server-side)
  or an offline in-memory mock CMS; jsdom test suite

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

package.json

@@ -0,0 +1,38 @@
+{
+  "name": "cms-onpageeditor",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "description": "Injectable on-page editor for the go-graph-cms: side-loaded onto the statically rendered page, edits through POST /api/edit.",
+  "scripts": {
+    "dev": "vite",
+    "dev:mock": "CMS_MODE=mock vite",
+    "build": "tsc --noEmit && vite build --mode lib",
+    "preview": "vite preview",
+    "typecheck": "tsc --noEmit",
+    "test": "vitest run",
+    "test:watch": "vitest"
+  },
+  "dependencies": {
+    "@mdi/js": "^7.4.47",
+    "@tiptap/core": "^3.27.1",
+    "@tiptap/extension-image": "^3.27.1",
+    "@tiptap/markdown": "^3.27.1",
+    "@tiptap/pm": "^3.27.1",
+    "@tiptap/starter-kit": "^3.27.1",
+    "marked": "^17.0.1",
+    "react": "^19.2.0",
+    "react-dom": "^19.2.0"
+  },
+  "devDependencies": {
+    "@testing-library/react": "^16.3.0",
+    "@types/node": "^22.0.0",
+    "@types/react": "^19.2.0",
+    "@types/react-dom": "^19.2.0",
+    "@vitejs/plugin-react": "^5.0.0",
+    "jsdom": "^26.0.0",
+    "typescript": "^5.9.0",
+    "vite": "^7.0.0",
+    "vitest": "^3.2.0"
+  }
+}