[Install] Validate public install path on a clean macOS environment

[Longfellow1]

Background

The current install surface is being consolidated around Homebrew + KeyPulse CLI lifecycle commands. Before public distribution, the flow needs to work on a clean Mac without requiring users to understand repo internals.

Task

Validate the public install path and document any failures.

Acceptance criteria

• Fresh install can run keypulse --help
• keypulse install init or the equivalent lifecycle command initializes runtime state
• keypulse doctor gives actionable output
• launchd jobs point to the installed keypulse executable, not a developer checkout
• README quick start matches the validated flow