feat(basecamp-cli): add installer

[ryanburnette]

Summary

• Adds a webi installer for basecamp-cli — the official CLI for Basecamp 3
• Includes releases.js, install.sh, install.ps1, and README.md
• Updates test/install.sh per contributing guidelines

Details

releases.js: Fetches from basecamp/basecamp-cli GitHub releases. Filters out .deb, .rpm, .apk, .sbom.json, checksums.txt*, .pem, .sig, and .bundle assets — keeping only the .tar.gz and .zip archives.

install.sh: Installs the bare basecamp binary from the archive root to ~/.local/opt/basecamp-cli-v$VERSION/bin/basecamp. Also copies the bundled shell completions (completions/) to the versioned opt directory. Parses basecamp version X.Y.Z for version detection.

install.ps1: Windows equivalent — extracts zip, installs basecamp.exe, copies completions.

README.md: Cheat sheet covers auth setup, listing projects/todos, creating and completing todos, posting messages, moving cards through workflow columns, per-project config (.basecamp/config.json), and shell completion setup.

test/install.sh: Added basecamp-cli to the rm/opt list and basecamp to the rm/bin list, and basecamp-cli to the webi test list — all in alphabetical order.

Checklist

• Ran npm run fmt (prettier + shfmt pass; pwsh-fmt skipped — no pwsh installed locally)
• Ran npm run lint (jshint + shellcheck pass; pwsh-lint skipped)
• Tested releases.js output — versions are clean semver, OS/arch detected correctly, download URLs resolve
• Updated test/install.sh
• Semantic commit messages