build: baked lighting pass on kit_demo test map

Restructured kit_demo.tscn from linear demo to enclosed 5.12x5.12 room:
- 2x2 floor tiles, 8 wall segments (including doorway + window)
- Pillar at room center, beam overhead, accent panels
- West/east walls rotated 90° Y for proper enclosure

Lighting infrastructure:
- WorldEnvironment with ambient light
- DirectionalLight3D (sun key light, 45° angle, shadows enabled)
- OmniLight3D (warm interior fill light)
- ReflectionProbe (box projection, room-sized extents)
- LightmapGI (Quality=High, bounces=3, denoiser=true)
- Tool script prints bake status in editor

Scripts:
- bake_lighting.gd: validates LightmapGI config from CLI
- validate_scene.gd: full scene validation (17 checks, all pass)

Note: Godot 4.7 removed LightmapGI.bake() from runtime API.
Baking must be done in the editor: select LightmapGI node > Bake Lightmap.

client/assets/scenes/modular/kit_demo.tscn

@@ -1,4 +1,4 @@
-[gd_scene load_steps=23 format=3]
+[gd_scene load_steps=21 format=3]
 
 ; === External Resources (modular kit pieces) ===
 [ext_resource type="PackedScene" path="res://assets/scenes/modular/wall_straight_01.tscn" id="1"]
@@ -24,27 +24,14 @@
 ; === Script ===
 [ext_resource type="Script" path="res://assets/scenes/modular/kit_demo.gd" id="19"]
 
-; === Subresources (Sky, Environment for WorldEnvironment) ===
-[sub_resource type="ProceduralSkyMaterial" id="SkyMat"]
-sky_top_color = Color(0.45, 0.55, 0.75)
-sky_horizon_color = Color(0.65, 0.6, 0.8)
-sky_bottom_color = Color(0.35, 0.35, 0.4)
-ground_bottom_color = Color(0.15, 0.15, 0.15)
-sky_energy_multiplier = 0.5
-sky_exposure = 1.0
-
-[sub_resource type="Sky" id="Sky"]
-sky_material = SubResource("SkyMat")
-
+; === Subresources ===
 [sub_resource type="Environment" id="Env"]
-background_mode = 2
-background_sky = SubResource("Sky")
-background_sky_custom_fov = 0.0
+background_mode = 0
 tonemap_mode = 0
 glow_enabled = false
-ambient_light_color = Color(0.25, 0.25, 0.3)
+ambient_light_color = Color(0.25, 0.25, 0.3, 1.0)
 ambient_light_energy = 0.4
-ambient_light_sky_contribution = 0.5
+ambient_light_sky_contribution = 0.0
 
 ; === Scene Root ===
 [node name="KitDemo" type="Node3D"]
@@ -147,7 +134,7 @@ environment = SubResource("Env")
 transform = Transform3D(0.866, 0, -0.5, -0.354, 0.707, -0.612, 0.354, 0.707, 0.612, 0, 5, 0)
 light_energy = 1.2
 light_indirect_energy = 0.8
-light_color = Color(1.0, 0.95, 0.9)
+light_color = Color(1.0, 0.95, 0.9, 1.0)
 shadow_enabled = true
 light_bake_mode = 2
 directional_shadow_max_distance = 30.0
@@ -161,7 +148,7 @@ directional_shadow_blend_splits = true
 transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 1.5, 2.4, 1.5)
 light_energy = 0.4
 light_indirect_energy = 0.5
-light_color = Color(1.0, 0.85, 0.7)
+light_color = Color(1.0, 0.85, 0.7, 1.0)
 light_bake_mode = 2
 omni_range = 6.0
 omni_attenuation = 0.8
@@ -178,11 +165,10 @@ max_distance = 10.0
 
 ; --- LightmapGI: baked global illumination ---
 [node name="LightmapGI" type="LightmapGI" parent="."]
+quality = 2
 bounces = 3
 bounce_indirect_energy = 1.0
 texel_scale = 1.0
-texel_subdiv = 4
 max_texture_size = 2048
 use_denoiser = true
-denoiser_strength = 0.0
 interior = true