WebGL2-only: max simultaneous framebuffer color attachments (multiple-render-target/deferred rendering).
WebGL2-only: max layers in a TEXTURE_2D_ARRAY (used by this engine's TextureArray/terrain atlasing).
WebGPU's own per-fragment-stage sampled-texture budget. Kept as its OWN field rather than
folded into MAX_TEXTURE_IMAGE_UNITS -- that field is Math.max()'d across WebGL1/WebGL2
probes taken unconditionally at init(), regardless of which renderer ends up active, so a
higher WebGL number can silently mask a lower real WebGPU one (exactly how a 20-texture WebGPU
bind group went undetected on a device whose WebGL2 context happened to report 32 units).
Supported numeric limits for hardware detection.