Feat/case filing document upload preview

[Nareshkumawat-star]

Description

Enables litigants to upload supporting documentary evidence (FIR copies, affidavits, property papers, contracts) during case filing and view uploaded documents using an in-browser PDF/Image previewer.

Type of Change

• New feature (non-breaking change which adds functionality)
• Documentation update
  ##Closes: [FEAT] Add case document upload and preview for litigants (PDF/image support) #1623

Key Changes Made

1. Backend Case Document Endpoint:
   • Added POST /api/v1/cases/{id}/documents endpoint in CaseManagementController.java to attach uploaded files directly to cases.
   • Enforces 10MB file size limits and PDF/JPG/PNG file validation.
2. Frontend File Upload Validations:
   • Updated FileUnifiedPage.jsx to enforce max 5 files, 10MB per file size limit, and supported document formats.
3. In-Browser Document Preview:
   • Updated CaseDetailPage.jsx to render a Preview button with an embedded PDF viewer iframe and Image Lightbox modal for JPG/PNG files.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes

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