feat: add labs command discovery

[peyton-alt]

Summary

• add visible entire labs discovery command for experimental workflows
• list entire review under labs while keeping the runnable command path as entire review
• keep review hidden from root help and label it as a labs entry in command help

Verification

• env GOCACHE=/private/tmp/entire-review-go-cache go test ./cmd/entire/cli ./cmd/entire/cli/review -run 'Test.*(Labs|Lab|ReviewCmd_Help|RootHelp)' -count=1
• env GOCACHE=/private/tmp/entire-review-go-cache go test ./cmd/entire/cli ./cmd/entire/cli/review -count=1
• mise run lint
• mise run check
• ./entire --help
• ./entire labs
• ./entire labs review
• ./entire review --help
• ./entire lab