fix: set homebrew cask name to kh

[eskp]

Summary

• GoReleaser defaults the cask name to the Go module name (cli) when no explicit name field is set in homebrew_casks
• This caused the generated cask to be Casks/cli.rb instead of Casks/kh.rb, making brew install keeperhub/tap/kh fail
• Adds name: kh to the homebrew_casks config so the next release publishes as kh.rb

Test plan

• Merge to main, wait for release-please PR
• Merge release PR, confirm goreleaser generates Casks/kh.rb in homebrew-tap repo
• Run brew tap keeperhub/tap && brew install keeperhub/tap/kh
• Verify kh version prints the tagged version