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/studio/src/stores/app.ts

@@ -0,0 +1,19 @@
+import { atom } from 'nanostores'
+
+export interface Toast {
+  id: string
+  message: string
+  type: 'success' | 'error'
+}
+
+export const $toasts = atom<Toast[]>([])
+
+export const addToast = (message: string, type: 'success' | 'error' = 'success') => {
+  const id = Math.random().toString(36).slice(2)
+  $toasts.set([...$toasts.get(), { id, message, type }])
+  setTimeout(() => removeToast(id), 4000)
+}
+
+export const removeToast = (id: string) => {
+  $toasts.set($toasts.get().filter(t => t.id !== id))
+}