Ease edit code #37965

Description

Let developers edit a file's source in a Monaco code editor side panel, without leaving the screen they're on:

• Content Drive: "Edit Source" in a .vtl file's row menu (right-click or ⋮).
• Page editor: choosing a file from a contentlet's VTL menu opens it in the same panel instead of Edit Content.

Save writes a new working version (it does not publish). Starts with .vtl; other code files (css, js, html, json…) come later.

Acceptance Criteria

• "Edit Source" in Content Drive opens a .vtl file in Monaco with Velocity highlighting
• Choosing a VTL file in the page editor's VTL menu opens the same editor instead of Edit Content
• Save (button or Cmd/Ctrl + S) creates a new working version; closing with unsaved changes asks first

Priority

Medium