Visuality project water lighting edit

- Added underwater volumetric godrays in shaders/composite.fsh using the existing shadow map.
- Godray intensity follows daylight, the sun direction, view direction, and shadow visibility.
- Added animated sunlight caustics to shaders/gbuffers_terrain.fsh for geometry below Y=63.
- Caustic projection follows the current world-space sun direction and moves over time.
- Caustics fade with water depth and only appear when direct sunlight reaches the surface.
- Existing water reflections/SSR, border fog, daylight color grading, and dynamic cloud lighting remain intact.

Static checks performed: balanced braces/parentheses and required source files present.
In-game visual testing is still required for final tuning.
