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/materials/waterfall.gdshader

@@ -0,0 +1,21 @@
+shader_type spatial;
+render_mode blend_mix, depth_draw_opaque, cull_back, diffuse_burley, specular_schlick_ggx;
+
+uniform float scroll_speed : hint_range(0.0, 5.0) = 2.0;
+
+void vertex() {
+}
+
+void fragment() {
+	vec2 uv = UV;
+	uv.y += TIME * scroll_speed;
+	float pattern = fract(uv.y * 4.0);
+	pattern = smoothstep(0.3, 0.7, pattern);
+	pattern = mix(0.4, 1.0, pattern);
+	vec3 base_color = mix(vec3(0.6, 0.85, 0.9), vec3(1.0, 1.0, 1.0), pattern);
+	ALBEDO = base_color;
+	ALPHA = mix(0.3, 0.7, pattern);
+	EMISSION = vec3(0.36, 0.52, 0.54) * 0.35 * pattern;
+	METALLIC = 0.0;
+	ROUGHNESS = 0.2;
+}