fix(session): resend bare /<skill> commands as /skill:<name>

[eliottness]

OmO rejects /impeccable with unknown_command because it only knows skills as /skill:<name>, while OpenChamber invokes them as /<name>. The user saw:

UnknownError: Unknown command /impeccable. Did you mean /skill:impeccable? Resend with "unknownCommandAsText": true to send it as text.

Changes

• PiRpcClient now keeps errorCode and errorData on failed responses (they were dropped).
• dispatchPrompt resends once as /skill:<name> <args> when the failure is unknown_command and OmO's suggestions contain exactly skill:<name>. OmO rejects unknown commands before admission, so the same clientMessageId is reused. Other unknown commands still surface the error.

Verification

• New endpoint test: POST /session/:id/command {command: "impeccable"} reaches the agent as /skill:impeccable polish it.
• npm run check: 645/645 pass.
• Live OmO probe: /humanizer say hi -> unknown_command with suggestions: ["skill:humanizer"]; resending /skill:humanizer say hi with the same clientMessageId -> disposition: started.