INDEPENDENT LIGHTING REBUILD

- EXPOSURE_MULTIPLIER was removed from shaders.properties and final.fsh.
- Daylight, twilight (morning/evening), night, cave, and block-light controls
  now live in lib/independent_lighting.glsl and are applied to individual
  light contributions instead of multiplying the final image.
- The old colortex2 per-pixel exposure mask path was removed from final.fsh.
- Sky and block light are sampled separately from the lightmap LUT.
- This prevents block light from whitening whole pixels and prevents lightmap
  masks from shimmering at geometry edges.
- Bloom threshold was raised so ordinary cloud highlights do not dominate bloom.
- Cloud source HDR was reduced slightly to preserve cloud detail.
- Fixed final BASE_SCENE_SCALE preserves the previous daytime HDR normalization
  without coupling night/cave/block brightness to a user exposure slider.


Root cause fixed from the screenshot:
- The previous final pass used a per-pixel lightmap mask to multiply the whole image.
- Sky pixels had no colortex2 metadata, so they were incorrectly classified as cave pixels.
- The block-light mask could therefore lift whole pixels to white and shimmer along geometry edges.
- The new implementation never applies block/cave/night multipliers to the final image.
