bug: prompt recording in responses interceptors wrongly records prompts

[pawbana]

Recording prompt should only care about last message, not last user message:

• aibridge/intercept/chatcompletions/paramswrap.go

  Line 55 in e164b50

  // We only care if the last message was issued by a user.

• aibridge/intercept/messages/paramswrap.go

  Lines 61 to 64 in e164b50

  	msg := b.Messages[len(b.Messages)-1]
  	if msg.Role != anthropic.MessageParamRoleUser {
  	return nil, nil
  	}

Make responses interceptor

aibridge/intercept/responses/base.go

Line 143 in e164b50

func (i *responsesInterceptionBase) lastUserPrompt() (string, error) {

consistent.