adds a 'git: view commit' – accepting a ref (e.g. HEAD, an sha, etc) to
more easily navigate to the git commit view.

<img width="3024" height="1888" alt="Screenshot 2025-09-26 at 21 43
09@2x"
src="https://github.com/user-attachments/assets/c001baec-66c2-46e5-b4a7-f691631f4166"
/>


if a bad ref is entered, the user is shown a generic error

<img width="2734" height="1442" alt="Screenshot 2025-09-27 at 21 04
52@2x"
src="https://github.com/user-attachments/assets/abdbd92d-ef0b-4de9-afb9-e9e52607dfdd"
/>

happy to adjust any of that. also worth noting is the `git: branch`
command UI is a bit nicer, can e.g. show you some metadata on the commit
before you select it, so happy to take it further in that direction if
desired, but thought i'd keep it simple to start.

Release Notes:

- Added view commit command palette action

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Co-authored-by: Cole Miller <cole@zed.dev>
Co-authored-by: Christopher Biscardi <chris@christopherbiscardi.com>
Co-authored-by: Marshall Bowers <git@maxdeviant.com>