Add ability to override a shortcut reserved for a menu item

[oashrafouad]

When a user assigns a shortcut that's reserved system-wide, the "Use Anyway" option allows them to override it. This PR extends that behavior to shortcuts reserved by menu items as well.

[sindresorhus]

Thanks for the PR. I think this should be opt-in (disabled by default) for a few reasons:

1. Backward compatibility - Current behavior blocks menu conflicts. Changing this silently could surprise existing apps.

2. Different intent - System shortcuts are external constraints the app can't control, so letting users override makes sense. Menu shortcuts are deliberate app design choices - if I assigned ⌘S to Save, I want it to work.

Something like: https://github.com/sindresorhus/KeyboardShortcuts/pull/226/changes#diff-41fc3abd80062ae3c8634038c89a3495bcd1d2455c1ff5cd5aa022f3409c6d8dR6