Align doctor with daemon status

[CoreyRDean]

Non-technical summary

i doctor now tells the user whether the background daemon is running, absent by choice, or installed but unhealthy. This matters because the daemon is a core part of the warm-start experience, and before this change doctor could not explain that state at all.

Technical summary

• add a daemon health probe to cmdDoctor using the existing control socket and service-install detection
• report not running (optional) when the daemon is absent, since the daemon is opt-in
• fail the daemon check when a service is installed but not responding, or when the daemon reports an unhealthy status
• avoid runtime/model/config path checks when state directory resolution fails
• add focused tests for optional absence, unhealthy installed daemon, running daemon status, and doctor output
• verify with /opt/homebrew/bin/go test ./...
• breaking changes: none

Additional notes

• This is a bounded doctor-alignment change only; it does not redesign doctor output or add GPU diagnostics.
• The remaining gap versus the full spec is that GPU diagnostics are still unimplemented and should be handled separately.