GPT-5.4 support and new voice interview controls

• GPT-5.4 model support Added OpenAI's GPT-5.4 with a much larger context window, plus reasoning and vision. Now the recommended model in the model selector.
• Context usage indicator in chat A circular progress indicator in the chat input shows how much of the model's context window your conversation is using, with a tooltip for details.
• Voice interview controls Added mute/unmute and end-conversation buttons, a new "Left Early" status for participants who hang up, and clearer visual states for voice input.
• Stronger email verification Sign-in code throttling is now per-email and more reliable, with clearer feedback when codes are rate-limited and more secure code generation.

Preview interview sign-in When an existing session conflicts with preview interview sign-in, you now get a warning before the session is cleared.

Voice reconnect stability Voice connections no longer get stuck during startup or reconnects, with bounded retries, clearer error messages, and reliable recovery from connection failures.