Catch invalid hotkey

[SteveLauC]

Looks like Coco won't complain if the given hotkey is invalid; it accepts and simply writes an error log:

[07-29 09:19:45] [ERR] [webview] Invalid hotkey format: "A+Command", an hotkey should have the modifiers first and only one main key, for example: "Shift + Alt + K"

Screen.Recording.2025-07-29.at.9.24.06.AM.mov