Filtering in Shortcut Guide

### Description of the new feature / enhancement

In Shortcut Guide, if that is active...while you are pressing keys, you intercept...and ask you press key(s), the list filters down to whatever keys are pressed.

### Scenario when this would be used?

You partially remember a keyboard shortcut and want to find it quickly. Or you know shortcut but want to tell someone 'official' name of it.

### Supporting information

_No response_

The issue names Shortcut Guide but no files, tests, or entry points. Start by locating the Shortcut Guide implementation and its keyboard-input handling, then define how the displayed shortcut list should narrow for pressed keys and verify that behavior.

Written by the indexing model from the issue text.