Activity Context Menu

It would be great if we can add support for right-clicking activities in the designer and having options like:

- Delete
- Clone / Copy / Cut / Paste (when right-clicking the canvas)
- Start of Workflow / Trigger Workflow (depending on whether the activity is a trigger or not)

Start by locating the designer's activity and canvas interaction entry points, since no specific files or tests are named. Review how activities, triggers, and the canvas currently handle selection and commands. Done means a right-click menu exposes the requested delete, clipboard, and workflow-start actions in the stated contexts.

Written by the indexing model from the issue text.