Feature request: Support newlines with Shift+Return in chat

In chat, entering Shift+Return currently submits my prompt. I'd like to be able to enter newline characters with Shift+Return instead to facilitate multi-line prompts. This is a well-established convention in web interfaces (see e.g. Claude).

Of course, the new `/editor` feature to allow prompts to be entered in a proper editor (#1029) is much appreciated, but Shift+Return could save me from some context-switching.