feat: add support for git branch via ssh and shorthand URLs

[dingruoqian99]

Summary

Added support for pulling from specific git branches using the #branch suffix in SSH URLs and GitHub shorthand.

Problem/Background

The CLI previously only supported branch selection for GitHub/GitLab HTTPS URLs formatted like .../tree/branch. Users could not specify a branch when using SSH URLs or shorthand syntax, which is essential for private repositories or specific development branches.

Solution

• Updated parseSource to recognize the # fragment as a git ref (branch/tag/commit).
• Handled SSH and shorthand URLs to preserve the branch information.
• Updated fetchSkillFolderHash to use the specified branch when checking for updates on GitHub.
• Added comprehensive tests for SSH branch formats and shorthand branch formats.

Testing

• Added unit tests in tests/source-parser.test.ts
• Verified with manual test script for various URL formats
• Ran full test suite to ensure no regressions

[dingruoqian99]

This PR resolves #394

[dingruoqian99]

@quuu trouble you to take a look at this

[quuu]

@dingruoqian99 im currently working on moving away from needing the tree folder hash (using the github API) which would also remove the need to hardcode and check main/master/ default branch

Let me see if i can go ahead with the more future proof change, before merging this