fix: Can not add skills in non-main branch

[kuainx]

fix #106

1. add branch name parse owner/repo[@ref]
2. add fetch default branch name with github api

Announcement: I'm not expert in Rust, code generated by AI, and tested with some cases by me.

[eljulians]

@kuainx thank you so much for the contribution! I'll have a look into this and merge it this weekend! Don't worry about the failing checks

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.73%. Comparing base (a84d668) to head (39d57f5).

Files with missing lines	Patch %	Lines
crates/cli/src/commands/add.rs	0.00%	18 Missing ⚠️
crates/sources/src/resolver.rs	75.86%	7 Missing ⚠️
crates/cli/src/main.rs	89.47%	2 Missing ⚠️

❌ Your patch check has failed because the patch coverage (80.00%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #112      +/-   ##
==========================================
- Coverage   92.44%   91.73%   -0.72%     
==========================================
  Files          39       39              
  Lines       18737    18840     +103     
==========================================
- Hits        17322    17282      -40     
- Misses       1415     1558     +143     

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