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

assets/data/block/template.toml

@@ -7,3 +7,4 @@ is_cross_plane = false
 is_transparent = false
 is_discard = false
 is_blend = false
+is_transitional = false