Align release workflow and GoReleaser config with fastgit

[kooksee]

Summary

• Update the GitHub release workflow to use the built-in token with write permissions
• Pin the GoReleaser action to v2-compatible syntax
• Rename GoReleaser build, release, and metadata values from fastcommit to fastgit
• Update the release download link to the new repository name

Testing

• Not run (not requested)

[gemini-code-assist]

Code Review

This pull request updates the .goreleaser.yaml configuration file to rename the project from 'fastcommit' to 'fastgit'. This change updates the build ID, binary name, ldflags project metadata, GitHub repository name, and the installation documentation link. There are no review comments, and I have no feedback to provide.

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