Proposal: Add Korean localization support using String Catalog

[cymise]

Hi,

I am working on adding Korean localization to the Settings UI.

Before submitting a pull request, I would like to confirm the preferred direction:

• Use Xcode String Catalog (.xcstrings)
• Replace String titles with LocalizedStringKey
• Keep English as default and add ko localization

Would you prefer:

1. String literal keys (e.g., "Simple Modifications")
   or
2. Structured keys (e.g., "sidebar.simple_modifications")?

Also, is there any existing localization guideline I should follow?

Thank you.

[cymise]

https://github.com/cymise/Karabiner-Elements/tree/i18n_kr