Update install guidance and always-on service docs

[DjDeveloperr]

Summary

• Add a global npm postinstall welcome message that points users at the Codex skill, the VS Code extension, and simdeck service on
• Update README and installation docs to use the NativeScript/SimDeck repo path and recommend the always-on LaunchAgent flow
• Make simdeck service discoverable in the CLI docs and clarify the difference between daemon and service

Testing

• Formatting checks passed for the edited Markdown, JSON, and script files
• cargo check passed for the Rust CLI after exposing service publicly
• Verified the postinstall welcome message output for global installs