Plugin UI components gain an autoFocus prop

What

Plugin UI components used when rendering plugin panes gained new props:

• Button now accepts action (must be one of the engine's existing keybinding actions, such as app:cycleDiffBase or app:diffFileListDown; engine-only keys like ctrl+c/ctrl+d still can't be rebound), plus a dimColor boolean.
• Button, Input, and Select all gain an autoFocus prop.

Why

Plugin authors building custom UI panes can now make a button trigger an existing app action, dim button text, and have a component automatically receive focus when it appears, without writing custom focus-handling logic.