CI: install nodejs for WASM smoke test, fix PATH

The WASM smoke test needs `node` for post-link.mjs and the WASI
runtime, but it's not available in the devx shell. Install nodejs
via nix-env alongside jq/unzip/zstd in the wasi-sdk setup step,
and add ~/.nix-profile/bin to the smoke test PATH.

Author: angerman

.github/workflows/nix-ci.yml

@@ -785,10 +785,13 @@ jobs:
         export PATH="$HOME/.nix-profile/bin:/nix/var/nix/profiles/default/bin:$PATH"
         # Verify required tools or install them (use nix-env, not nix profile,
         # because experimental features may not be enabled in the VM)
-        for tool in jq unzip zstd; do
+        # nodejs is needed for the WASM smoke test (post-link.mjs + WASI runtime)
+        for tool in jq unzip zstd node; do
           if ! command -v "$tool" &>/dev/null; then
-            echo "Installing $tool via nix-env..."
-            /nix/var/nix/profiles/default/bin/nix-env -iA "nixpkgs.$tool"
+            pkg="$tool"
+            [ "$tool" = "node" ] && pkg="nodejs"
+            echo "Installing $pkg via nix-env..."
+            /nix/var/nix/profiles/default/bin/nix-env -iA "nixpkgs.$pkg"
           fi
         done
         curl -fsSL https://gitlab.haskell.org/ghc/ghc-wasm-meta/-/raw/master/bootstrap.sh | \
@@ -826,7 +829,7 @@ jobs:
       shell: devx {0}
       run: |
         set -eo pipefail
-        export PATH=$PATH:$HOME/.ghc-wasm/wasi-sdk/bin
+        export PATH="$HOME/.nix-profile/bin:$PATH:$HOME/.ghc-wasm/wasi-sdk/bin"
         echo 'main = putStrLn "Hello from WASM backend"' > /tmp/hello.hs
         _build/dist/bin/wasm32-unknown-wasi-ghc /tmp/hello.hs -o /tmp/hello.wasm