Add Korean interface localization and Hangul font support (#857)

* Show Thai file names and text in the interface with an installed Thai font

A drawing whose file name is Thai showed boxes in its file tab and in the
window title: the interface loaded one Latin system font (plus a CJK font for
the Chinese interface), and neither has Thai.

install_fonts now also adds an installed Thai font (Thonburi, Leelawadee UI,
Noto Sans Thai, Loma...) after the Latin one, in any interface language, since
file names and drawing text are Thai whatever the interface is in. No font is
bundled; without one installed nothing changes.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

* Add Korean interface localization and Hangul font support

---------

Co-authored-by: Chanthawat Kiriyadee <[email protected]>
Co-authored-by: Claude Opus 5.5 <[email protected]>
Co-authored-by: Brandon Thomas <[email protected]>

docs/control-protocol.md

@@ -152,7 +152,10 @@ Select a language with `engine.execute` and the UI command `ui.language`:
 {"id":1,"method":"engine.execute","params":{"command":"ui.language","params":{"lang":"uk"}}}
 ```
 
-Supported values are `auto`, `en`, `uk`, `pt-BR`, `de`, `es`, `cs`, `ru`, `fr`, `zh` and `it` (Chinese needs an installed CJK font; without one the result's `shown` is `en`). `ui.set` also accepts
+Supported values are `auto`, `en`, `uk`, `pt-BR`, `de`, `es`, `cs`, `ru`, `fr`, `zh`, `it` and `ko`.
+Chinese needs an installed CJK font; Korean needs a font covering the Korean interface from the
+optional craft-fonts input or the operating system. Without a suitable font, the saved choice is
+retained and the result's `shown` is `en`. `ui.set` also accepts
 `{"interfaceLanguage":"uk"}`; `ui.inspect` reports the saved choice in its UI state.
 Invalid choices leave the current language unchanged. Menus, command labels and prompt text
 returned by the control channel retain their English source text. See [localization.md](localization.md).