fix: replace bluish gray backgrounds with pure black for dark mode

[ad1tyayadav]

📝 Description

This PR updates the dark mode background colors across the website.
Previously, dark mode used bluish-gray tones (bg-gray-800 / bg-gray-900), which appeared slightly off-black.
Now, all dark backgrounds have been unified to pure black (#000000) for a cleaner and more consistent look.

This is a UI improvement that enhances visual contrast and makes dark mode more OLED-friendly.

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🔗 Related Issue

Fixes #486

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🔄 Type of Change

• 🎨 UI/UX Update (visual changes, styling improvements)
• 🐛 Bug Fix

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📷 Visual Changes

• Before

• After

💭 Additional Notes

This PR makes only the necessary updates to replace hardcoded bg-gray-800 and bg-gray-900 with bg-black.
It affects multiple sections and components (AboutUs, Try, Donation, etc.) but does not modify layout or logic.
Visually, the site now has a smoother dark theme with better contrast and a true black background.

Thank you for reviewing! 🎉

[github-actions]

🎉 All Checks Passed!

Status: ✅ Ready to merge

✅ Completed Workflows

Workflow	Status	Details
🔨 Continuous Integration	✅ Passed	Build completed successfully
📝 Code Linting	✅ Passed	All formatting and style checks passed

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🚀 This PR is ready for review and can be safely merged to main branch!

Great work! Your code meets all quality standards. 👏

[FirePheonix]

alright, so this is a big PR since we're looking at all designs of all pages of dark mode.. might take some time to review.

[github-actions]

🎉 All Checks Passed!

Status: ✅ Ready to merge

✅ Completed Workflows

Workflow	Status	Details
🔨 Continuous Integration	✅ Passed	Build completed successfully
📝 Code Linting	✅ Passed	All formatting and style checks passed

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🚀 This PR is ready for review and can be safely merged to main branch!

Great work! Your code meets all quality standards. 👏

[ad1tyayadav]

@FirePheonix hello brother please let me know if anything need from my end.

[FirePheonix]

@ad1tyayadav
I tested out your PR many times... but somehow the black design is not that much better than the current bluish shade of dark mode. We'd need some gradient/ other shade of black, or some pattern along side the dark mode would do equally good maybe. Designs always go through last minute changes.
Sorry for taking this much time, but right now we'll be looking other possible better designs that can be proposed for the dark mode.
But you're free to work on other things for now.
And if you feel like there can be a better dark mode for this, feel free to propose.