Plan: WP Rdius field selected by default when switching to screen

It seems like MP's puts the cursor into the "WP Radius" field when the user switches to the Plan screen. This is dangerous because it means if the user presses a key (especially a number) the field can be cleared which leads to issues (e.g. https://github.com/ArduPilot/ardupilot/issues/15070) where the WPNAV_RADIUS field is set incorrectly.

I think it would be best if no fields are selected by default when switching to the Plan screen.

Reproduce the issue by switching to the Plan screen and checking whether the WP Radius field receives focus. Trace the screen-switch focus handling and verify that no field is selected by default, including after keyboard input is sent immediately after switching.

Written by the indexing model from the issue text.