feat(gameplay): add Ocean biome with water generation and heightmap adjustments

- Introduce Ocean biome enum, builder, and detection logic.
- Add ocean water building to all existing biomes and modify heightmap thresholds for low mountainous areas.
- Skip cave and river generation in Ocean (and River) biomes; avoid carving water blocks.
- Comment out border blending call and update block fill logic.

CMakeLists.txt

@@ -124,6 +124,7 @@ add_executable(${PROJECT_NAME}
     src/gameplay/river_path.cpp
     src/block.cpp
     src/gameplay/vertex_data.cpp
+    src/gameplay/builders/ocean_builder.cpp
 )
 
 if(CMAKE_BUILD_TYPE STREQUAL "Debug")