fix: remove duplicate CSS blocks in index.css

[akhilmodi29]

Fixes #689

Problem
The css/index.css file had its entire content duplicated
3 times. This caused:

• CSS file size bloated from ~38KB to ~114KB
• Style conflicts due to duplicate rule definitions
• Browser having to parse 3x more CSS than needed
• Inconsistent styles when duplicate rules had differences

Fix
Removed the two duplicate CSS blocks keeping only the
first clean and complete copy of the stylesheet.

Testing

• All styles render correctly ✅
• No duplicate rules in CSS ✅
• File size reduced by ~66% ✅
• No style conflicts ✅

[akhilmodi29]

@Charushi06 Please review this PR and add the required labels including gssoc:approved. This fixes the duplicate CSS blocks bug in studyplan.

Labels suggested:

• level:beginner
• type:bug
• quality:clean