* feat(renderer): add fog effect based on render distance
* refactor(gameplay): remove dead code and simplify chunk neighbor context
Remove the large commented-out `init_chunks()` function, and eliminate the `affected_neighbor` tracking in `gen_chunks_internal()`. This simplifies the neighbor context building and removes unused vertex data regeneration for affected neighbors.
* refactor(gameplay): move chunk generation phases into gen_chunk method
Consolidate multiple phase generation calls into a single gen_chunk() method on Chunk, which handles neighbor generation and ensures thread safety. Simplify World::gen_chunks_internal by using gen_chunk() instead of manual phase orchestration.
* fix(gameplay): use gen_phase_one to get seed
* feat(world): integrate thread pool and async chunk generation
* fix(renderer): correct shader uniform name and remove unused uniform
* feat(gameplay): add temporary chunk flag to prevent path clearing
* fix: add thread safety for cave and river path mutexes
* refactor: remove unused uniforms and set cameraPos uniform outside lambda
* feat(world): add dynamic thread pool resizing
* feat(world): add thread pool size management and UI controls
* feat(world): add ChunkLoadStyle enum and rename chunk_pos to get_chunk_pos
* feat(player): add configurable fly Y speed
* refactor(world): add thread pool start/stop and auto-detect threads
Extract thread pool starting and stopping into dedicated methods. Set default pool threads to 0 to enable automatic detection of available cores, and ensure thread pool is properly managed during world rebuild.
* fix: include shared_mutex header
* fix(gameplay): simplify set_chunk_load_style switch and fix fallthrough bug
* fix(world): add missing include for <utility>
