feat(baseBranch): improve `shortName` calculation

[matthewevans]

🧢 Changes

• Renamed original shortName getter to lastPathComponent to better reflect its actual functionality
• Added an enhanced implementation of shortName that properly handles Git reference formats
• Added support for stripping common Git prefixes (refs/remotes/remoteName/, remoteName/, refs/heads/)

☕️ Reasoning

The previous shortName implementation only extracted the last path component of a branch name without handling Git's reference formats properly. The new implementation normalizes branch names by intelligently stripping Git-specific prefixes based on context (remote vs. local), resulting in more consistent and user-friendly branch name representation throughout the application.

Further context:

• This affected me when I had my target set to origin/release/2025.18. When I tried to create a PR it was attempting to use 2025.18 as the base branch. GitHub refused and GitButler showed an error. This fix allowed me to successfully create the PR. I also invested the other locations that leveraged shortName and they all appeared to use it in a context where they would expect the full branch name.

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[Byron]

That's great, thanks so much! It would be lovely if this could fix the linked PR-creation issue. Do you think it's possible to add a simple task list to the PR so it's possible to see what's missing? Maybe even turn it into a draft. The reason I am asking is that the new shortName() function doesn't seem to be used yet. Thanks again

CC @estib-vega .

[matthewevans]

That's great, thanks so much! It would be lovely if this could fix the linked PR-creation issue. Do you think it's possible to add a simple task list to the PR so it's possible to see what's missing? Maybe even turn it into a draft. The reason I am asking is that the new shortName() function doesn't seem to be used yet. Thanks again

CC @estib-vega .

Forgive me if I'm misunderstanding, but the new shortName function (that's been renamed) is just a copy of the old shortName.

1. Renamed shortName to lastPathComponent
2. Implemented a fixed version of shortName that works with branches that contain /. This is the actual fix of this PR.
3. lastPathComponent is left purely for posterity (if there's a use-case that desires just the last part of the branch path).

[estib-vega]

@matthewevans another great contribution! Much appreciated :)

[Caleb-T-Owens]

We should probably use the rust function given_name for this since remove names can include forward slashes