Introduce shadow mapping using a dedicated depth framebuffer and shader. The block fragment shader now performs percentage-closer filtering (PCF) with Poisson disk sampling and random rotation for soft shadows. The vertex shader outputs light-space coordinates. A new depth shader pair handles rendering from the light's perspective, discarding transparent fragments. The renderer sets up the light projection based on the camera position and sun direction, and applies the shadow factor to diffuse lighting. Day/night cycle can now be toggled off in the world server thread.
* refactor: update water texture
* feat(gameplay): implement transparent block rendering with depth sorting
* fix(world): use camera pos for distance calculations, make water passable
* refactor(player): use ivec3 for block pass check
* feat(camera): add underwater detection
* feat(renderer): add underwater effect with framebuffer post-processing
* feat(block): add gas property and refactor solid block check
* fix(assets): set leaf block transparency to false
* fix(block): set leaf as transparent
