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/test_simple.gd

@@ -0,0 +1,14 @@
+extends Node
+
+var count := 0
+
+func _ready():
+	print("_ready called")
+	set_process(true)
+
+func _process(delta):
+	count += 1
+	print("_process #", count, " delta=", delta)
+	if count >= 5:
+		print("Quitting")
+		get_tree().quit()