[Refactor][Server] Introduce unified document architecture and simplify backend export system

[Gautam25Raj]

Summary

This PR restructures the backend architecture by introducing a unified document system and simplifying export and sharing workflows across the platform.

Refactor

Unified Document Architecture

• Replaced resume-specific models with a generic Document model

• Added support for multiple document types:

  • Resumes
  • Cover letters
  • Portfolios
  • Link in bio pages

• Removed legacy resume and resume share link tables

• Unified document handling across the platform

Sharing System Improvements

• Replaced resume-specific sharing with generic shared document links
• Merged share and shares routes into a single route structure
• Added shared/public document link types

Backend Service Refactor

• Moved controller business logic into dedicated services
• Improved maintainability and separation of concerns

Enhancement

Export Workflow Simplification

• Removed backend Playwright rendering
• Removed BullMQ export queues and workers
• Migrated export generation to frontend using React PDF

Cleanup & Improvements

• Added document validators
• Updated configuration and environment examples
• Improved type safety and linting across the server

Notes

• No major user-facing breaking changes
• Focused on maintainability, scalability, and backend simplification
• Establishes foundation for supporting multiple document types

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📝 Documentation update
• 🧪 Tests (adding or updating tests)

Checklist

• I have read the CONTRIBUTING.md document.
• 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.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• Any dependent changes have been merged and published in downstream modules.