Cache npm dependencies

Editor assessment

The subject states the change plainly: npm dependencies are now cached in CI. The perf type is exactly right, and the ci scope locates the surface. The body, however, is a single emoji-prefixed line that restates the subject verbatim, contributing nothing; the caching mechanism, key strategy, or measured speedup would have been the useful content, and for a performance change the measured effect is the most interesting fact. The PR reference is well formed. Style is otherwise clean. Clear subject, empty body: valid and understandable, but mediocre in teaching value.