Let the shortcuts search box capture a key combo directly

[Basit-Balogun10]

Instead of only matching by action name, the search box now live-captures an actual key combo when it's focused (e.g. hold Ctrl+Shift, press C), showing it as "Ctrl + Shift + ..." while modifiers are held and filtering the list to whatever's bound to it once the final key lands. Typing a plain character still falls back to the old keyword search.

Fixes #882

Demo:

search-keyboard-shortcuts-cosmic-term.mp4

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