Show the real cause of CLI connection errors

When a station could not reach its TofuPilot instance, the CLI printed a generic "error sending request" message with no way to tell what actually failed.

• Fixed connection errors to report the underlying cause, such as a rejected TLS certificate, a DNS failure or a proxy issue
• Added the full error chain to the message, for example "invalid peer certificate: UnknownIssuer" when the instance certificate is not trusted