Function initializeGpuByteBudget

Configure the shared budget for whichever supported viewer entry point starts first.

• undefined → use the config default; this is no opinion after another entry point has configured the budget, so it is ignored silently.
• null or NaN → auto-size from ambient memory signals; NaN warns.
• 0 → disable byte-budget eviction (unbounded resident geometry).
• a positive number → pin the budget to exactly that many bytes.

Later explicit requests are ignored with a warning because the budget is module-global and shared by every pool and LOD registry on the page.