feat: add multi-lingual support & accessibility improvements

[adityasingh-0803]

This PR introduces two major enhancements to SaralSeva:

1. Multi-lingual support: added language files (English, Hindi) and a language-switcher interface; updated all user-facing UI text to use translation keys.
2. Accessibility improvements: semantic HTML with ARIA attributes, high-contrast mode toggle, WCAG-compliant colors, keyboard navigation support.

Additional changes:

• Documentation updated with instructions for translation and accessibility guidelines.
• Styling updates to support accessibility modes.
• Minor UI adjustments to ensure readability on mobile/low-resolution devices.

These changes make SaralSeva more inclusive and usable for a wider range of users, especially in rural and multi-lingual settings.

[github-actions]

Thank you for raising this issue!

We'll review it as soon as possible. We truly appreciate your contributions! ✨

Meanwhile make sure you've visited the README.md, CONTRIBUTING.md, and CODE_OF_CONDUCT.md before creating a PR for this. Also, please do NOT create a PR until this issue has been assigned to you. 😊

[eccentriccoder01]

Go ahead @adityasingh-0803!