[VPAT-16] improvement: add file validation to prevent malicious uploads

[prateekshourya29]

Description

Add client-side checks for double extensions, dangerous file types, dot files, and path traversal patterns. Addresses security audit recommendations for file upload validation.

Type of Change

• [x] Improvement (change that would cause existing functionality to not work as expected)

Summary by CodeRabbit

Release Notes

• New Features
  • Added security checks to block files with dangerous executable and script extensions from being uploaded
  • Implemented strict filename validation to prevent uploads of empty names, hidden files, and path-traversal attacks
  • Enhanced detection to identify suspicious double file extensions

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