SML Docs: Add detailed Panini Projection guide for first-person equipment (cleaned)

[Rovetown]

This PR introduces a comprehensive guide for Panini Projection in Unreal Engine / Satisfactory, targeting first-person equipment rendering.

Changes include:

• Executive Summary for quick reference (pro-level TL;DR)
• Beginner-friendly explanations of Panini Projection and why it’s necessary
• Detailed workflow instructions:
  • Apply Panini Projection via Material Attributes (Master Material + Instances)
  • Direct Panini Projection for one-off materials
• Explanation of FOV limitations and why alignment breaks above 90°
• Best practices, including a Master Material tip for scalable setups
• Images for:
  • Panini workflow comparison (Apply vs Direct)
  • Projection comparison (Panini on vs off)
  • FOV range examples (70°, 90°, 120°)

This guide is intended to serve both new modders and experienced users, offering both full explanations and quick lookup information.