fix: improve UI spacing and contrast on subjects section

[Ragini613]

Related Issue

Fixes #309

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Description

Improved UI spacing and visual contrast on the Subjects section:

• Increased contrast on available subject cards using a darker background and bolder dark text
• Replaced low-opacity styling on "Coming Soon" cards with a dedicated lighter background and properly readable dark text, instead of using opacity which reduced readability
• Made the "Browse Subjects" heading responsive across screen sizes (text-4xl to text-7xl based on breakpoint)
• Added proper spacing below the heading for better visual balance

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Type of Change

• UI/UX improvement

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Screenshots / Demo

Tested locally on localhost:3000 — contrast and readability significantly improved on both available and "Coming Soon" subject cards across all semesters.

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How Has This Been Tested?

Ran the project locally using npm run dev, navigated to the Subjects section, and visually verified spacing and contrast improvements across multiple semester sections and screen sizes.

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Checklist

• My code follows the project structure and conventions
• I have tested the changes locally
• I have linked the related issue properly
• No existing functionality was broken

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AI Usage

• I have used AI tools (ChatGPT, Copilot, Claude, etc.) and I have reviewed, verified, and understood all generated code/content before submitting this PR

If AI tools were used, briefly explain how:

Used Claude for guidance on identifying contrast/spacing issues and suggesting Tailwind class improvements. Reviewed and tested all changes locally before submitting.

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[Ragini613]

Hi @pushkarscripts, just following up on this PR — it's ready for review whenever you get a chance. Happy to make any changes if needed. Thank you! 🙂