fix(tui): preserve prompt input when navigating to new session

[ariane-emory]

Description

Previously, when starting a new session, if there was text in the prompt input text box, this text would be retained.

However, changes introduced in the commit 29f7dc0 seems to have clobbered this behaviour.

A PR to resolve this regression is forthcoming.

Plugins

None

OpenCode version

1.4.11

Steps to reproduce

1. During a session, enter some text in the prompt input text box.
2. Hit the key that you have bound to the session_new command.
3. Observe that the text has disappeared from the prompt input text box.

Screenshot and/or share link

N/A

Operating System

N/A

Terminal

N/A