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/BridgeBlockout.tscn

@@ -0,0 +1,33 @@
+[gd_scene load_steps=5 format=3]
+
+[sub_resource type="StandardMaterial3D" id="Material_deck"]
+albedo_color = Color(0.62, 0.55, 0.44, 1)
+roughness = 0.8
+
+[sub_resource type="BoxMesh" id="Mesh_deck"]
+material = SubResource("Material_deck")
+size = Vector3(8, 0.2, 3)
+
+[sub_resource type="StandardMaterial3D" id="Material_support"]
+albedo_color = Color(0.45, 0.42, 0.38, 1)
+roughness = 0.85
+
+[sub_resource type="CylinderMesh" id="Mesh_support"]
+material = SubResource("Material_support")
+top_radius = 0.2
+bottom_radius = 0.2
+height = 1.0
+
+[node name="BridgeBlockout" type="Node3D"]
+
+[node name="Deck" type="MeshInstance3D" parent="."]
+position = Vector3(0, 0.6, 0)
+mesh = SubResource("Mesh_deck")
+
+[node name="SupportL" type="MeshInstance3D" parent="."]
+position = Vector3(-3.2, 0, 0)
+mesh = SubResource("Mesh_support")
+
+[node name="SupportR" type="MeshInstance3D" parent="."]
+position = Vector3(3.2, 0, 0)
+mesh = SubResource("Mesh_support")