fix: resolve scene dependency errors and missing UID in main.tscn

- WaterBody.tscn, WaterfallBody.tscn: gdshader files were referenced
  with type="Material" instead of type="Shader". Wrapped each
  shader in a ShaderMaterial sub-resource so Godot can load them.
- ChimneySmoke.tscn: reordered sub-resources so StandardMaterial3D
  is defined before QuadMesh that references it.
- WaterfallMist.tscn: fixed node type GpuParticles3D -> GPUParticles3D
  (case-sensitive class name in Godot 4.7).
- jajce_world.gd: added explicit Vector3 type annotation to fix
  'Cannot infer the type of pos variable' parse error.
- main.tscn.uid: created missing UID mapping file. The scene header
  declared uid="uid://rs3hv73svbpa" but no .uid file existed,
  causing Godot to reject the scene as unsupported format.

world/jajce/ChimneySmoke.tscn

@@ -19,17 +19,17 @@ scale_max = 0.6
 color = Color(0.8, 0.8, 0.8, 0.6)
 alpha_curve = SubResource("2")
 
-[sub_resource type="QuadMesh" id="4"]
-size = Vector2(1, 1)
-material = SubResource("5")
-
-[sub_resource type="StandardMaterial3D" id="5"]
+[sub_resource type="StandardMaterial3D" id="4"]
 albedo_color = Color(1, 1, 1, 1)
 transparency = 1
 shading_mode = 0
 billboard_mode = 1
 cull_mode = 0
 
+[sub_resource type="QuadMesh" id="5"]
+size = Vector2(1, 1)
+material = SubResource("4")
+
 [node name="ChimneySmoke" type="GPUParticles3D"]
 emitting = true
 amount = 16
@@ -37,5 +37,5 @@ lifetime = 3.0
 one_shot = false
 local_coords = true
 process_material = SubResource("3")
-draw_pass_1 = SubResource("4")
+draw_pass_1 = SubResource("5")
 draw_order = 1