Translate code md to bangla

[noruzzamans]

Motivation for the change, related issues

This PR continues the Bengali (Bangla) translation effort for WordPress Playground documentation. It adds the translation for the "Code contributions" page (/contributing/code).

Related to ongoing i18n work for the bn locale.

Implementation details

• Translated packages/docs/site/docs/main/contributing/code.md to Bengali
• Followed the existing translation format with HTML comments containing original English text
• Used consistent transliteration style matching other Bengali translations (e.g., কন্ট্রিবিউশন, কন্ট্রিবিউট, প্লেগ্রাউন্ড)
• Kept technical terms and Docusaurus syntax keywords (like :::info, :::tip) in English