[readme] use tilde expansion instead of "$HOME" for consistency

[readme] use "$HOME" instead of hardcoded "/home/user"

[meta] Align and enhance AGENTS.md instructions

[actions] upgrade vampire/setup-wsl

[Docs] Clean up wording in docs and shell comments

[Docs] fix CONTRIBUTING grammar

[readme] Revise Node.js version usage examples

[Tests] fix 4 test failures

[meta] run `npm run doctoc`

[Fix] `install.sh`: check `mkdir` return codes

[Fix] `install.sh`: fix POSIX compliance, printf format strings, and profile detection

[Fix] `nvm which`: show alias name in infinite loop error message

[Fix] `nvm uninstall`: fix alias cleanup glob expansion

[Fix] `nvm debug`: use default empty values for potentially unset variables

[Fix] `nvm_iojs_version_has_solaris_binary`: fix comparison to detect non-iojs versions