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/WaterfallMist.tscn

@@ -0,0 +1,28 @@
+[gd_scene load_steps=3 format=3]
+
+[sub_resource type="Curve" id="Curve_alpha"]
+_data = [Vector2(0, 1), Vector2(1, 0)]
+
+[sub_resource type="ParticleProcessMaterial" id="ParticleProcessMaterial_mist"]
+lifetime_randomness = 0.2
+spread = 180.0
+gravity = Vector3(0, -0.5, 0)
+initial_velocity_min = 0.3
+initial_velocity_max = 0.8
+scale_min = 0.1
+scale_max = 1.5
+color = Color(0.85, 0.95, 0.95, 0.4)
+alpha_curve = SubResource("Curve_alpha")
+emission_shape = 1
+emission_box_extents = Vector3(2.5, 1.0, 0.5)
+
+[node name="WaterfallMist" type="GpuParticles3D"]
+emitting = true
+amount = 48
+lifetime = 2.5
+one_shot = false
+preprocess = 1.0
+speed_scale = 1.0
+local_coords = true
+draw_order = 0
+process_material = SubResource("ParticleProcessMaterial_mist")