ShadowOnly v12
Target: Minecraft 1.19.4 + Iris 1.6.11 + Sodium 0.4.10

Based directly on the working V6 baseline.

Changes from V6:
- shadowDistanceRenderMul: 1.0 -> 1.25, keeping normal shadow-pass culling but moving the caster boundary farther away to reduce visible culling strips.
- Shadow bias: 0.00075 -> 0.0018 to reduce self-shadow acne / diagonal striping on large surfaces.
- PCF radius: 0.35 -> 0.20 for a slightly crisper shadow edge.
- Shadow map remains 2048x2048 for UHD 620-class performance.

No shadow distortion and no culling-disabling hacks are used in this version.
