feat: performance budget profiling setup

- docs/performance-budget.md: 60fps/2GB VRAM budget with CPU, GPU,
  memory, and draw-call targets (P95<16.6ms, P99<50ms)
- scripts/profiling/: SceneTree + Node profilers, test scenes
- scripts/generate_occluders.gd: auto-generate OccluderInstance3D
  from CSG wall pieces (128^3 voxel occlusion culling)
- scripts/convert_csg_to_mesh.gd: CSG->StaticMesh baker with LOD
  slots (LOD1@15m, LOD2@30m)
- project.godot: occlusion culling + LOD settings enabled
- modular scene UV2 data from lightmapping pass
- rcon_command_handler.gd conflict resolved (kept upstream plugin cmd)
- Fixed profiler_node.gd warmup frame bug (60 frames, not 3)
- Fixed convert_csg_to_mesh.gd LOD API (add_lod + distance)

client/scripts/profiling/profiler_scene.tscn

@@ -0,0 +1,6 @@
+[gd_scene format=3]
+
+[ext_resource type="Script" path="res://scripts/profiling/profiler_node.gd" id="1"]
+
+[node name="Profiler" type="Node"]
+script = ExtResource("1")