fix: improve mobile layout in index.html

[asthamalviya14]

Description

Improved the mobile responsiveness of the index.html page.
Updated the layout to provide a better user experience on smaller screens.

Related Issue

Fixes #1610

Type of change

• Bug fix
• New feature / enhancement
• Documentation update
• Test addition
• Refactor

Checklist

• I have read CONTRIBUTING.md
• My branch is up to date with main
• I have run pytest -v and all tests pass
• I have not introduced duplicate issues or features
• My PR title follows the format: feat/fix/docs/test: short description
• I have added tests for new features (Level 2 and 3 issues)
• No hardcoded secrets or API keys in my code
• This PR is linked to a GSSoC 2026 issue

Screenshots (if frontend change)

Added mobile layout improvements.

Test evidence

pytest -v
- [ ] Refactor

## Checklist
<!-- All boxes must be checked before requesting review -->
- [ ] I have read [CONTRIBUTING.md](../CONTRIBUTING.md)
- [ ] My branch is up to date with `main`
- [ ] I have run `pytest -v` and all tests pass
- [ ] I have not introduced duplicate issues or features
- [ ] My PR title follows the format: `feat/fix/docs/test: short description`
- [ ] I have added tests for new features (Level 2 and 3 issues)
- [ ] No hardcoded secrets or API keys in my code
- [ ] This PR is linked to a GSSoC 2026 issue

[imDarshanGK]

@asthamalviya14
Add demo video showing the working features

[asthamalviya14]

Recording.2026-07-24.182928.mp4

The hero title is now clearly visible in light mode while the dark theme remains unchanged,this video demonstrates the updated hero title contrast in light theme.

[asthamalviya14]

Hi,I've added the requested demo video to this PR. Kindly review it .Thank you!

[imDarshanGK]

@asthamalviya14 Please add a demo showcasing the mobile layout improvements, as this issue is focused on responsive changes. The current demo only shows the light and dark themes.