feat(world): open up the dive site fog and match the horizon colour

Lighter fog and volumetric fog, brighter key and ambient light, terrain
tiles visible to 420 m (60 m fade), and a background colour equal to
the fog colour times its energy so culled tiles never read as a dark
band. The seabed shader culls back faces again now that the tiles are
wound front-face up.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

game/world/sites/dive_site.tscn

@@ -5,10 +5,10 @@
 
 [sub_resource type="Environment" id="EnvironmentUnderwater"]
 background_mode = 1
-background_color = Color(0.005, 0.045, 0.065, 1)
+background_color = Color(0.034, 0.12, 0.144, 1)
 ambient_light_source = 3
 ambient_light_color = Color(0.12, 0.32, 0.37, 1)
-ambient_light_energy = 0.42
+ambient_light_energy = 0.55
 glow_enabled = true
 glow_levels/1 = 1.0
 glow_levels/2 = 1.0
@@ -20,11 +20,11 @@ glow_hdr_threshold = 1.0
 fog_enabled = true
 fog_light_color = Color(0.07, 0.25, 0.3, 1)
 fog_light_energy = 0.48
-fog_density = 0.014
+fog_density = 0.006
 fog_height = -4.0
 fog_height_density = 0.025
 volumetric_fog_enabled = true
-volumetric_fog_density = 0.025
+volumetric_fog_density = 0.01
 volumetric_fog_length = 72.0
 
 [node name="DiveSite" type="Node3D"]
@@ -36,7 +36,7 @@ environment = SubResource("EnvironmentUnderwater")
 [node name="AmbientDirection" type="DirectionalLight3D" parent="."]
 rotation_degrees = Vector3(-52, -24, 0)
 light_color = Color(0.39, 0.65, 0.7, 1)
-light_energy = 0.38
+light_energy = 0.75
 shadow_enabled = true
 
 [node name="Terrain" type="StaticBody3D" parent="."]