Refactor: Implement global error handling and clean up controllers (Fixes #447)

[Jivan-Patel]

🐛 Description

This PR addresses issue #447 by introducing a global error-handling middleware to the Express application and refactoring all backend controllers to adhere to the DRY (Don't Repeat Yourself) principle.

Previously, every controller manually wrapped its logic in a try/catch block and returned a hardcoded 500 response. This resulted in duplicated code (35+ occurrences) and inconsistent error responses across the application.

✅ Changes Made

• Created middlewares/errorHandler.js: A global Express error-handling middleware that catches errors passed via next(err) and sends a unified, consistent JSON response. It also securely handles stack traces by omitting them in production.
• Updated server.js: Registered the errorHandler middleware securely at the bottom of the middleware stack (right after the API routes).
• Refactored 8 Controllers: Replaced all redundant res.status(500) manual catch blocks with next(error) in the following controllers:
  • authController.js
  • aiController.js
  • questionController.js
  • resumeController.js
  • sessionController.js
  • userSheetProgressController.js
  • achievementController.js
  • jobController.js

🎯 Benefits

• Eliminates 35+ duplicated catch blocks across the codebase, resulting in cleaner controllers focused purely on business logic.
• Guarantees consistent error responses for all API endpoints.
• Establishes a single centralized place to add logging, monitoring (e.g., Sentry), or alerting in the future.

Fixes #447

[KaranUnique]

@Jivan-Patel Please take a look on security issue by github ai

[Jivan-Patel]

@KaranUnique, The vulnerability flagged by the GitHub Advanced Security CodeQL has been resolved. So please review and merged my PR.