Add Khmer (README.km.md) localization (#1198)

* Create README-kh.md for Khmer localization

Add Khmer language support to README

* Address review feedback: rename to README.km.md, add screenshots/star history

- Rename README-kh.md to README.km.md (correct ISO 639-1 language code, dot separator)
- Add Khmer link to main README.md language switcher
- Add feature screenshot table matching original README structure
- Add browser keyboard shortcuts note
- Add Star History section
- Use relative image paths consistent with other localized READMEs

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Co-authored-by: im4tta <82812618+im4tta@users.noreply.github.com>

README.md

@@ -8,7 +8,7 @@
 </p>
 
 <p align="center">
-  English | <a href="README.zh-CN.md">简体中文</a> | <a href="README.zh-TW.md">繁體中文</a> | <a href="README.ko.md">한국어</a> | <a href="README.de.md">Deutsch</a> | <a href="README.es.md">Español</a> | <a href="README.fr.md">Français</a> | <a href="README.it.md">Italiano</a> | <a href="README.da.md">Dansk</a> | <a href="README.ja.md">日本語</a> | <a href="README.pl.md">Polski</a> | <a href="README.ru.md">Русский</a> | <a href="README.bs.md">Bosanski</a> | <a href="README.ar.md">العربية</a> | <a href="README.no.md">Norsk</a> | <a href="README.pt-BR.md">Português (Brasil)</a> | <a href="README.th.md">ไทย</a> | <a href="README.tr.md">Türkçe</a>
+  English | <a href="README.zh-CN.md">简体中文</a> | <a href="README.zh-TW.md">繁體中文</a> | <a href="README.ko.md">한국어</a> | <a href="README.de.md">Deutsch</a> | <a href="README.es.md">Español</a> | <a href="README.fr.md">Français</a> | <a href="README.it.md">Italiano</a> | <a href="README.da.md">Dansk</a> | <a href="README.ja.md">日本語</a> | <a href="README.pl.md">Polski</a> | <a href="README.ru.md">Русский</a> | <a href="README.bs.md">Bosanski</a> | <a href="README.ar.md">العربية</a> | <a href="README.no.md">Norsk</a> | <a href="README.pt-BR.md">Português (Brasil)</a> | <a href="README.th.md">ไทย</a> | <a href="README.tr.md">Türkçe</a> | <a href="README.km.md">ភាសាខ្មែរ</a>
 </p>
 
 <p align="center">