docs: add README translations for 10 languages (12 total)

Add machine-translated README files for Japanese, Korean, Spanish,
French, German, Portuguese (BR), Turkish, Arabic, Hindi, and Russian.
Update language selector in English and Chinese READMEs to link all 12
versions.

New files: README.{ja,ko,es,fr,de,pt-BR,tr,ar,hi,ru}.md
Modified: README.md, README.zh-CN.md (language selector bar)

README.zh-CN.md

@@ -2,7 +2,7 @@
 
 # Skill Seekers
 
-[English](https://github.com/yusufkaraaslan/Skill_Seekers/blob/main/README.md) | 简体中文
+[English](README.md) | 简体中文 | [日本語](README.ja.md) | [한국어](README.ko.md) | [Español](README.es.md) | [Français](README.fr.md) | [Deutsch](README.de.md) | [Português](README.pt-BR.md) | [Türkçe](README.tr.md) | [العربية](README.ar.md) | [हिन्दी](README.hi.md) | [Русский](README.ru.md)
 
 > ⚠️ **机器翻译声明**
 >