feat: add RTU Kota CSE syllabus (Sem 1-8) + fix download & preview bug

[aryan24cse109-dev]

📚 What this PR does

Adds complete syllabus data for Rajasthan Technical University (RTU) Kota
— Computer Science Engineering department, covering all 8 semesters.

Also fixes two critical bugs in Syllabus.js that were present for all entries.

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🐛 Bugs Fixed

1. Download button was not working

The handleDownload function was only showing an alert() popup instead of
actually downloading the file. Fixed with proper anchor-click download method.

2. Preview button had no functionality

The Preview button had no onClick handler at all. Added handlePreview
function that opens the PDF in a new browser tab.

3. Subjects section showing empty heading

For entries with no subjects listed, "Subjects Covered:" heading was still
rendering with empty content. Added conditional rendering to hide it when
subjects array is empty.

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✅ Changes Made

• Added 8 PDF files to client/public/pdf/:
  • RTU_CSE_Sem1.pdf to RTU_CSE_Sem8.pdf
• Fixed handleDownload function in Syllabus.js
• Added handlePreview function in Syllabus.js
• Added fileUrl field to all existing syllabusData entries
• Added 8 new data entries for RTU Kota CSE (Semester 1 to 8)
• Added conditional rendering for empty subjects section

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🏫 College Details

Field	Value
University	Rajasthan Technical University Kota
Department	Computer Science Engineering
Semesters	1st to 8th
Source	Official RTU Website

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🧪 Tested

• ✅ Locally tested on localhost:3000
• ✅ University filter → RTU Kota shows only CSE department
• ✅ Download button → PDF saves to device
• ✅ Preview button → PDF opens in new tab
• ✅ Empty subjects section hidden for RTU entries

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📌 Note

This is the first of multiple planned contributions for RTU Kota.
After this PR, similar PRs will follow for other departments (IT, ECE, ME, Civil etc.)

Closes #447

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