[Polish] Profile and optimize: pooling, occlusion, LOD, GPU instancing

[sja-thedude]

Goal\n60fps on a mid-tier GPU at 1080p.\n\n## Tasks\n- Frame Debugger pass on each scene\n- Object pool common spawns\n- Bake occlusion + tune LOD groups

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Part of the NEXUS: The Sentient Galaxy initiative under PlayPath. Project lives at /projects/nexus-sentient-galaxy/.