AquaReal V6 — Metals + Sky-Exposed Rain Puddles

Changes:
- Keeps the existing block.properties metal classification.
- Reworked metal response to avoid neon/over-bright omni-light reflections.
- Metal terrain now uses AquaReal's existing ray-marched screen-space reflection
  path plus neutral sky fallback and Fresnel response.
- Rain puddles only appear on nearly horizontal terrain with high Minecraft skylight.
  This prevents terrain under roofs/block cover from becoming wet.
- Puddles use the same reflection_calc()/fastRaymarch() path used by AquaReal water,
  so visible nearby terrain can appear in the reflection.
- Rain reflection remains neutral/near-white rather than blue.

Limitation:
- This is screen-space reflection, so off-screen objects cannot appear in the
  reflection. It is not hardware ray tracing.
- Shader-only rain cannot store a true one-minute wetness history after rain ends
  without a persistent buffer/state design; this version ties wetness to rainStrength.
