Add Bangla (bn) Localization Support

[Md-Sifatullah617]

💡 Motivation and Context

The feedback package did not support Bangla, which is needed for apps like Charge.AI serving Bangladeshi users.

💚 How did you test it?

• Manually tested in a demo Flutter app using BetterFeedback widget.
• Switched device/app locale to bn and verified translated text.

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes (manual for now)
• I updated the docs if needed (README.md for new locale mention)
• All tests passing (if applicable)
• No breaking changes

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🔮 Next steps

• Consider adding support for other RTL languages like Urdu.
• Improve UI adaptability for translated text with longer phrases.

[Md-Sifatullah617]

Hi @ueman @Saad29 👋
As requested, this PR includes only the Bangla (bn) translation changes — all unrelated modifications have been removed.
Thanks again for reviewing and guiding me through the process. Let me know if there's anything else you'd like me to adjust. 🙏
Looking forward to your feedback! 😊

[Saad29]

Translation looks good

[ueman]

Thanks again 🙌