🧪 [Core] Add End-to-End Document Rendering Tests

[ahmdkaml]

🧪 Overview

Add integration tests covering the complete document rendering pipeline.

🎯 Goals

Verify that a document can travel through the complete system:

Document
   ↓
Modules
   ↓
Template
   ↓
Features
   ↓
Rendering
   ↓
Preview / PDF

📦 Requirements

Tests should cover representative documents containing:

Multiple module types
Module features
Nested modules
Multiple pages
Template configuration

The tests should verify that:

All document content is rendered.
Module ordering is preserved.
Features are reflected in the output.
Pagination behaves correctly.
Preview and PDF use equivalent document/layout information.
🌱 Goal

Prevent changes to the Core rendering system from silently breaking the document output.