🐛 Expand the node base image through a named stage

COPY --from= resolves its value as a stage name at parse time, before build
args exist, so COPY --from=node:${NODE_VERSION} collapsed to the invalid
'node:' and docker failed with 'failed to parse stage name'. ARGs in global
scope are expanded in FROM, so route through a named nodebase stage; the
per-stage ARG redeclaration keeps the tool-cache paths expanding.

cspell.json

@@ -28,6 +28,8 @@
         "runwisp",
         "glab",
         "hostedtoolcache",
+        "nodebase",
+        "frontends",
         "catthehacker",
         "nsnull",
         "dedup",