The active-runtime assertion required process.versions.node to equal
.nvmrc exactly, so any Node.js patch release broke `toolchain:check` and
the act CI run even though package.json engines (>=26.10.0 <27) supports
the newer runtime.
Keep .nvmrc and the Docker base image exactly pinned for reproducibility
(both still asserted), but validate the running runtime against the
engines range instead. Verified: toolchain:check, lint, typecheck,
i18n:check, hk:matrix:check and all 3391 tests pass.
openhands