refactor: move studio to frontends workspace

- Move studio from root to frontends/studio/
- Add owner-tools frontend for live blog admin UI
- Add shared ui component library
- Set up npm workspaces for frontends
- Add enhanced code block extension for editor

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontends/package.json

@@ -0,0 +1,14 @@
+{
+  "name": "writekit-frontends",
+  "private": true,
+  "workspaces": [
+    "ui",
+    "studio",
+    "owner-tools"
+  ],
+  "scripts": {
+    "dev:studio": "npm -w studio run dev",
+    "dev:owner-tools": "npm -w owner-tools run dev",
+    "build": "npm -w ui run build && npm -w studio run build && npm -w owner-tools run build"
+  }
+}