os.availableParallelism() reports host CPUs rather than a container's
CPU quota (256 against a 64-CPU quota here), so local defaults spawned
255 Vitest forks (55 GiB peak RSS) and oversubscribed every scheduler.
scripts/parallelism.ts keeps the CPU count in CI and caps other runs at
12, or 48 for Vitest forks and the local coverage budget; documentation
and hygiene aggregates run up to 8 gates instead of 4. Explicit
DSH_GATE_CONCURRENCY, DSH_OXLINT_THREADS, DSH_COVERAGE_MAX_WORKERS, and
--maxWorkers still win.
Refs #5852
