build: baked lighting pass on kit_demo test map

- Restructured kit_demo.tscn from linear demo to enclosed 5.12x5.12 room
  with walls, floor tiles, pillar, beam, doorway, window
- Added WorldEnvironment with ProceduralSky for ambient lighting
- Added DirectionalLight3D (sun key light, 45° angle, shadows enabled)
- Added OmniLight3D (warm interior fill light)
- Added ReflectionProbe for interior specular reflections
  (box projection, room-sized extents)
- Added LightmapGI with balanced quality settings
  (bounces=3, texel_scale=1.0, max_texture_size=2048, denoiser=true)
- Added tool script (kit_demo.gd) that prints bake status in editor
- Added bake_lighting.gd CLI bake script (requires GPU-enabled instance)
- Updated project.godot with reflection atlas and shadow map quality settings

Headless baking note: Godot's standard editor build requires a GPU/display
for LightmapGI.bake(). Open the scene in the Godot editor and click 'Bake
Lightmap' on the LightmapGI node to generate the baked lightmap data.

client/assets/materials/floor_tile_01.tres

@@ -0,0 +1,17 @@
+[gd_resource type="StandardMaterial3D" load_steps=5 format=3]
+[ext_resource type="Texture2D" path="res://assets/textures/floor_tile_01/basecolor.png" id="1"]
+[ext_resource type="Texture2D" path="res://assets/textures/floor_tile_01/normal.png" id="2"]
+[ext_resource type="Texture2D" path="res://assets/textures/floor_tile_01/roughness.png" id="3"]
+[ext_resource type="Texture2D" path="res://assets/textures/floor_tile_01/metallic.png" id="4"]
+
+[resource]
+albedo_texture = ExtResource("1")
+normal_enabled = true
+normal_texture = ExtResource("2")
+normal_scale = 1.0
+roughness = 0.6
+roughness_texture = ExtResource("3")
+metallic = 0.0
+metallic_texture = ExtResource("4")
+texture_filter = 1
+uv1_scale = Vector3(2.0, 2.0, 1.0)