feat: improve doctor remediation and health summary UX

[dDevAhmed]

Summary

Implements CLI-022 by refining stellarforge doctor output around remediation and overall environment health.

Included

• explicit overall health states: ready, usable with warnings, action required, and no diagnostics registered
• preserves deterministic pass/warn/fail counts
• keeps warning-only runs non-fatal
• keeps required failures mapped to the existing diagnostic exit code
• renders remediation directly beneath affected checks
• extends mixed pass/warn/fail coverage
• adds explicit warning-only and all-pass behavior tests
• confirms unexpected secret-bearing check failures remain redacted and still receive safe remediation

Scope

No styling dependency, spinner, TTY-only behavior, or environment dump is introduced. Output remains plain-text and CI-safe.

Closes #25