Auto-detect and initialise the best available kernel.
Tries occt-wasm (the default kernel) first, then falls back to
brepjs-opencascade, then brepkit-wasm. occt-wasm loads via its
browser-safe OcctKernel.init() (auto-locates the .wasm via
import.meta.url), so no manual registration is required.
Idempotent — calling it again after a kernel is registered is a no-op that returns the current kernel ID immediately.
The kernel ID that was initialised ('occt-wasm', 'occt', or 'brepkit').
brepjs — Public API