Fix agent investigations for OpenVPN route setup errors

[eirenik0]

Summary

• retain recent log evidence in incident investigations and surface it in proxy2vpn agent investigate
• prioritize log evidence in investigator guidance to avoid unsupported auth/config conclusions
• detect OpenVPN route setup failures separately from config errors and tailor summaries/action plans around route-state review
• add coverage for CLI output, persisted investigation data, and route-error diagnostics

Testing

• Not run (not requested)

[chatgpt-codex-connector]

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