Description: Implement enhanced validation middleware for submission endpoints and file uploads.

Domain: Backend Development

Coding Difficulty: Beginner

Steps to reproduce (for bugs): N/A (Feature)

Expected outcome: Enhanced validation middleware provides better error messages. Submission endpoints validate URL format. PDF uploads enforce file size and type validation.

Links or references: WikiSourceVerifier GitHub

Setup Steps: See README.md for local development instructions

Subscribers: Eugene233, Udehb
Tags: WMA-HackChallenge-2025