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.

include/Cubed/gameplay/biome.hpp

@@ -15,6 +15,7 @@ enum class BiomeType {
     MOUNTAIN,
     RIVER,
     SNOWY_PLAIN,
+    OCEAN,
     NONE
 };
 

include/Cubed/gameplay/builders/biome_builder.hpp

@@ -13,5 +13,6 @@ public:
 protected:
     void build_bottom();
     void place_grass();
+    void ocean_water_build();
 };
 } // namespace Cubed

include/Cubed/gameplay/builders/ocean_builder.hpp

@@ -0,0 +1,23 @@
+#pragma once
+
+#pragma once
+
+#include "Cubed/gameplay/builders/biome_builder.hpp"
+namespace Cubed {
+
+class ChunkGenerator;
+
+class OceanBuilder : public BiomeBuilder {
+public:
+    OceanBuilder(ChunkGenerator& chunk_generator);
+    void build_biome() override;
+    ChunkGenerator& get_chunk_generator() override;
+    void build_vegetation() override;
+
+private:
+    ChunkGenerator& m_chunk_generator;
+
+    void build_blocks();
+};
+
+} // namespace Cubed