As a developer, I want a dedicated retry option on Duo Chat responses, so that I don't have to rephrase my question or hope natural language "try again" works. **Acceptance criteria:** Add a retry icon to the response action bar, after the existing copy button. - Given a completed or stopped Duo Chat response, when the user clicks the retry button, Duo resubmits the original prompt with the current conversation history. A new response streams in the main view. The retry consumes credits like any other response. - Given Duo Chat is actively streaming a response, no action buttons are visible. The user must stop generation before retrying. - Retry icon appears on every completed or stopped response - Does not appear on intermediate tool call steps - Action buttons (including retry) are hidden during streaming, same as today - User must stop generation before retry becomes available