Polish poolctl for public use

[cnberry]

Summary

• add matching hero art, README structure, operations/protocol/troubleshooting/roadmap docs, MIT license, security policy, and CI
• add an explicit private config override and write the adapter cache with mode 0600
• keep cleaner writes guarded, auto-cancel cleaner delay, and report post-write state
• align with switchctl and the shared language-neutral script/install contract
• replace legacy root scripts and requirements duplication with the installed package and pyproject metadata

Verification

• 13 unit tests
• Ruff format and lint
• detect-secrets baseline scan
• installer syntax and executable checks
• wheel build, CLI help, Markdown link, and current-tree privacy checks