chore: rename GitHub org from onkernel to kernel

[hiroTamada]

Summary

• Update Go module path from github.com/onkernel/hypeman-cli to github.com/kernel/hypeman-cli
• Update hypeman-go dependency to github.com/kernel/hypeman-go v0.9.0
• Update all Go source file imports to use new org name
• Update .goreleaser.yml Homebrew tap owner and homepage URL
• Update .github/workflows/release-doctor.yml repository check
• Update README.md installation instructions and links
• Update scripts (link, unlink, use-sdk-preview)
• Fix lint error in build.go (non-constant format string)

This PR fixes the broken GoReleaser release process after the GitHub organization rename from onkernel to kernel.

Test plan

• go build ./... succeeds
• go test ./... passes
• Verify GoReleaser workflow runs successfully on next release

---

Note

Migrates the project from onkernel to kernel and updates dependencies and tooling accordingly.

• Update module path to github.com/kernel/hypeman-cli and switch all imports to github.com/kernel/hypeman-go
• Bump SDK dependency to hypeman-go v0.9.0 and refresh go.sum
• Adjust release/packaging: .github/workflows/release-doctor.yml repo check, .goreleaser.yml Homebrew tap owner and homepage
• Update README.md install instructions and links
• Update scripts (scripts/link, scripts/unlink, scripts/use-sdk-preview) to reference new org
• Fix non-constant format string in pkg/cmd/build.go

^{Written by Cursor Bugbot for commit c175687. This will update automatically on new commits. Configure here.}