Precompute static shader math on the CPU for EffectStack

[Breakdown-Dog]

Objective

• Previously, values like inv_radius and aspect ratio corrections were calculated inside fragment shaders.
• This PR moves these calculations to the CPU (once per frame).

Solution

• Refactored EffectStack to precompute static/invariant math on the CPU side before binding uniforms, rather than computing them per-pixel in WGSL.

Additional Cleanup:

• Extracted the render pipeline setup logic from mod.rs into a dedicated pipeline.rs to keep the main module focused on effect parameters and CPU precomputation. Pure structural refactor, no behavioral changes.

Testing

• Example post-processing runs as expected.

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