fix: include fresnelSchlick chunk when refraction is enabled without specular

[willeastcott]

Summary

• Fixes a shader compilation error ('getFresnel' : no matching overloaded function found) when a material has refraction enabled but specular is effectively disabled (e.g. black specular color with no metalness)

Root Cause

The fresnelSchlickPS chunk — which defines the getFresnel() function — was only included inside the #ifdef LIT_SPECULAR_OR_REFLECTION guard in litForwardPostCode.js. However, the refractionDynamicPS chunk (included under #ifdef LIT_REFRACTION) calls getFresnel() regardless. When LIT_SPECULAR_OR_REFLECTION was false but LIT_REFRACTION was true, the function was called but never defined.

Fix

Moved the fresnelSchlickPS include so it is also triggered when LIT_REFRACTION is defined:

#if defined(LIT_SPECULAR_OR_REFLECTION) || defined(LIT_REFRACTION)
    #if LIT_FRESNEL_MODEL == SCHLICK
        #include "fresnelSchlickPS"
    #endif
#endif

Applied to both the GLSL and WGSL versions of litForwardPostCode.js.

Steps to Reproduce

1. Create a standard material with specular color set to black
2. Remove any environment map / skybox
3. Enable refraction (non-zero value) and enable dynamic refraction
4. Apply to a mesh — shader compilation fails

Test Plan

• Verify the above repro steps no longer produce a shader error
• Verify materials with specular + refraction still render correctly
• Verify materials with specular only (no refraction) are unaffected

[Copilot]

Pull request overview

Fixes a forward-lit shader compilation failure where refraction code can call getFresnel() even when the Fresnel implementation chunk wasn’t being included (notably when refraction is enabled while specular/reflection is effectively disabled).

Changes:

• Move fresnelSchlickPS inclusion out of the LIT_SPECULAR_OR_REFLECTION-only block.
• Include fresnelSchlickPS when either LIT_SPECULAR_OR_REFLECTION or LIT_REFRACTION is defined.
• Apply the same change to both GLSL and WGSL forward-pass post code.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/scene/shader-lib/wgsl/chunks/lit/frag/pass-forward/litForwardPostCode.js	Ensures the Fresnel Schlick chunk is available when refraction is enabled in WGSL.
src/scene/shader-lib/glsl/chunks/lit/frag/pass-forward/litForwardPostCode.js	Ensures the Fresnel Schlick chunk is available when refraction is enabled in GLSL.

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