WIP: feat(scene) integrate beauty pass — shader water, building blockouts, wind, smoke, 6 textures

- Add 3 missing Terrain3D textures: Dirt Path (id=3), Riverbank Stone (id=4),
  Compacted Ground (id=5) with procedural albedo PNGs + generate tool
- Replace greybox river BoxMesh with animated vertex-displacement water shader
- Replace greybox waterfall BoxMesh with scrolling-UV waterfall shader
- Add WaterfallMist GPUParticles3D with upward drift and alpha fade
- Add wind vertex shader for tree canopies (sin-based, height-weighted sway)
- Replace StylizedTree.tscn with script-driven procedural tree supporting
  3 canopy color variants and position-based randomization
- Replace greybox house boxes with StylizedHouse (walls + pitched roof + door)
- Replace mill box with StylizedMill (body + roof + water wheel cylinder)
- Replace fortress box with FortressBlockout (keep + parapet + corner turret)
- Replace bridge box with BridgeBlockout (deck + pillar supports)
- Add ChimneySmoke GPUParticles3D on each house roof
- Height-snap buildings (fortress + village) to terrain surface in _ready()
- Update JajceWorld.tscn: remove all greybox landmark sub-resources, instance
  new scenes, keep terrain/navigation/sky/fog as-is
- Update scaffold test for new scene structure and beauty elements

world/jajce/StylizedMill.tscn

@@ -0,0 +1,43 @@
+[gd_scene load_steps=7 format=3]
+
+[sub_resource type="StandardMaterial3D" id="Material_body"]
+albedo_color = Color(0.55, 0.38, 0.22, 1)
+roughness = 0.8
+
+[sub_resource type="BoxMesh" id="Mesh_body"]
+material = SubResource("Material_body")
+size = Vector3(3, 3, 4)
+
+[sub_resource type="StandardMaterial3D" id="Material_roof"]
+albedo_color = Color(0.55, 0.30, 0.18, 1)
+roughness = 0.75
+
+[sub_resource type="PrismMesh" id="Mesh_roof"]
+material = SubResource("Material_roof")
+size = Vector3(3.4, 1.2, 4.4)
+left_to_right = 0.5
+
+[sub_resource type="StandardMaterial3D" id="Material_wheel"]
+albedo_color = Color(0.20, 0.12, 0.06, 1)
+roughness = 0.7
+
+[sub_resource type="CylinderMesh" id="Mesh_wheel"]
+material = SubResource("Material_wheel")
+top_radius = 1.2
+bottom_radius = 1.2
+height = 0.15
+
+[node name="StylizedMill" type="Node3D"]
+
+[node name="Body" type="MeshInstance3D" parent="."]
+position = Vector3(0, 1.5, 0)
+mesh = SubResource("Mesh_body")
+
+[node name="Roof" type="MeshInstance3D" parent="."]
+position = Vector3(0, 3.6, 0)
+mesh = SubResource("Mesh_roof")
+
+[node name="WaterWheel" type="MeshInstance3D" parent="."]
+position = Vector3(-1.8, 1.5, 0)
+rotation_degrees = Vector3(0, 0, 90)
+mesh = SubResource("Mesh_wheel")