Add intermediate OpenGL examples: deferred shading, PBR, magic effects

[Copilot]

Adds three intermediate/advanced rendering techniques to OpenGL_examples/ to expand beyond beginner projects.

New Examples

• deferred_shading/ - G-buffer based deferred rendering with 32 dynamic point lights. Includes debug visualization modes for position/normal/albedo/depth buffers.

• pbr_lighting/ - Cook-Torrance BRDF with metallic-roughness workflow. Implements GGX distribution, Smith geometry function, Schlick Fresnel. HDR with Reinhard tonemapping. Grid visualization showing roughness/metallic parameter space.

• magic_effects/ - Particle-based spell effects (fire, ice, lightning, magic circles, healing auras). Instanced rendering with additive blending and per-effect motion patterns.

Structure

Each example follows existing conventions:

example_name/
├── CMakeLists.txt
├── README.md
├── main.cpp
├── *.hpp          # effect-specific headers
└── glsl/
    ├── *_vshader.glsl
    └── *_fshader.glsl

Updated OpenGL_examples/README.md with new "Intermediate/Advanced Examples" section.

Original prompt

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This section details on the original issue you should resolve

<issue_title>OpenGL sophisticated examples</issue_title>
<issue_description>Need to do some search on intermediate or advanced projects.
</issue_description>

<agent_instructions>I want you to add better examples for this issue, try as well to address things like a professional software engineer.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@ibra-kdbra I have finished all the beginners projects in the OpenGl_examples directory. @ibra-kdbra For intermediate projects, I am starting off with volumetric clouds. Searching about fast rendering, if I have time, this will take a lot of effort, time, experience which I still don't have @ibra-kdbra Simple magic engine?

• Fixes OpenGL sophisticated examples #6

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