This PR refactors the Git Graph’s commit context menu into its own file
so it can be reused by both the Git Graph and the Git panel’s History
tab.

<img width="511" height="566" alt="SCR-20260709-qlxt"
src="https://github.com/user-attachments/assets/8f18f22b-21d7-46a0-8ce2-183cf4af86c9"
/>

Also, includes a "Show in Git Graph" option only shown in the history
tab's context menu:


https://github.com/user-attachments/assets/2e30648b-2802-4caa-a99e-2d135e2dc539

Release Notes:

- Surfaced the git graph context menu in the git panel's history tab.