feat: ocean (#16)

* 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.

* fix(gameplay): re-enable border blending and protect water in cave gen

* refactor(generation): move ocean water build to later phase

* feat(block): add is_transitional property and refine border blending

* fix(block): set stone block as transitional

* fix(world): generate temporary chunks for surface blend neighbor data

* fix(gameplay): simplify block fill logic in blend_surface_blocks_borders

* refactor(tree): remove debug logging and unused include

src/gameplay/biome.cpp

@@ -62,6 +62,10 @@ std::string get_biome_str(BiomeType biome) {
         break;
     case SNOWY_PLAIN:
         str = "Snowy Plain";
+        break;
+    case OCEAN:
+        str = "Ocean";
+        break;
     case NONE:
         str = "Unknown";
         break;
@@ -190,6 +194,9 @@ BiomeType determine_biome(const BiomeConditions& conditions) {
     if (conditions.mountainous > 0.75) {
         return MOUNTAIN;
     }
+    if (conditions.mountainous < 0.25) {
+        return OCEAN;
+    }
     auto temp = conditions.temp;
     auto humid = conditions.humid;
     if (temp < 0.5) {