[GOOD FIRST ISSUE]: ML Model Endpoints Lack Timeout Protection

### Context

## Description
Fixed a critical issue where ML model endpoints and external API calls could hang indefinitely due to missing timeout handling.

## Problem
- Requests could run forever if models became unresponsive
- Flask worker threads were not released (resource exhaustion)
- Frontend showed infinite loading with no feedback
- One slow request could block the entire system

### What Needs to Be Done

- Added backend timeout wrapper for all ML and external API calls
- Introduced input validation and structured error handling
- Returned proper HTTP `504 Gateway Timeout` for long-running requests
- Implemented frontend request timeout using `AbortController`

### Resources

- [Contribution Guide - Start Here!](https://github.com/AOSSIE-Org/TODO/blob/main/CONTRIBUTING.md)
- [Discord Channel](https://discord.gg/hjUhu33uAn)

### Getting Started

- [x] I have joined the [Discord server](https://discord.gg/hjUhu33uAn) and will post updates there
- [x] I have read the [Contribution Guide](https://github.com/AOSSIE-Org/Template-Repo/blob/main/CONTRIBUTING.md)
- [x] I understand this issue is assigned on a first-come, first-served basis