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>

studio/embed_testing.go

@@ -1,18 +0,0 @@
-//go:build testing
-
-package studio
-
-import (
-	"io/fs"
-	"net/http"
-)
-
-var distFS fs.FS
-
-func Handler() http.Handler {
-	return http.NotFoundHandler()
-}
-
-func Read(name string) ([]byte, error) {
-	return nil, fs.ErrNotExist
-}