docs: add Korean translation of README (README.ko.md) and localized image

[stu442]

Description

This PR adds a Korean translation of the README.

• Added README.ko.md
• Inserted a language switcher at the top of README.md
• Added a localized image description_ko.svg for the Korean translation

Scope

• Translation covers the entire README
• keywords (@context, +project, (A)), and formatting are preserved
• description_ko.svg is referenced only in README.ko.md (the English README still uses the original image)

Notes

• Future updates to diagrams/images may also require syncing for description_ko.svg

[Copilot]

Pull Request Overview

This PR adds Korean localization support by creating a complete Korean translation of the README file and adding language navigation links.

• Added comprehensive Korean translation covering all content, format rules, and examples
• Introduced language switcher navigation links in both English and Korean README files
• Created localized Korean diagram image to support the translated content

Reviewed Changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 1 comment.

File	Description
README.md	Added language switcher navigation links at the top
README.ko.md	Complete Korean translation with localized content and image reference

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[karbassi]

For description.svg, use text, rather than paths. See https://github.com/todotxt/todo.txt/blob/master/description.svg for example.