[iOS] Read Aloud should support Bluetooth car audio and background playback

Feature request

Please make Read Aloud on ChatGPT for iOS work reliably with the active Bluetooth audio route, including a car's audio system, and continue safely when the device is locked or the app is in the background.

Use case

I often want to listen to a completed ChatGPT response—for example, a morning news or report summary—while driving. The response is already generated and visible on the iPhone. When the iPhone is connected to the car over Bluetooth, I should be able to start Read Aloud and listen hands-free without keeping ChatGPT in the foreground or interacting with the phone.

Desired behavior

• Route Read Aloud to the active iOS audio output, including Bluetooth car audio/A2DP.
• Continue playback when the screen is locked or ChatGPT moves to the background, where iOS allows it.
• Expose play/pause, resume, and playback position through the lock screen/Now Playing controls and compatible car controls.
• Preserve the playback position across interruptions and resume from the same point.
• Provide a clear state when the audio route or background playback is unavailable.
• Consider CarPlay support where appropriate.

Scope

This is separate from realtime Voice: it concerns reading a completed response that is already on the device. It is also complementary to #41829, which requests offline or connection-independent playback; this request focuses on Bluetooth routing, background audio lifecycle, and hands-free vehicle use.

Expected result

A user can start Read Aloud before driving, put the iPhone away, and continue listening through the car's connected audio system without manually keeping the app open or restarting playback.

No files or tests are named. Start by locating the iOS Read Aloud implementation and checking how it handles active audio routes, background or locked-device playback, interruptions, and Now Playing controls. Done means playback works through Bluetooth car audio, survives backgrounding where supported, preserves position, and reports unavailable states clearly.