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/WaterfallBody.tscn

@@ -0,0 +1,13 @@
+[gd_scene load_steps=3 format=3]
+
+[ext_resource type="Material" path="res://world/jajce/materials/waterfall.gdshader" id="1_waterfall_shader"]
+
+[sub_resource type="BoxMesh" id="Mesh_waterfall_body"]
+material = ExtResource("1_waterfall_shader")
+size = Vector3(5, 10, 0.5)
+
+[node name="WaterfallBody" type="Node3D"]
+position = Vector3(25, 5, -24)
+
+[node name="Mesh" type="MeshInstance3D" parent="."]
+mesh = SubResource("Mesh_waterfall_body")