build: use npm rather than pnpm

Most PL Typescript repos use `pnpm` but so far we've been using `npm`
and that's fine with me: all I care about is that the requirement is
codified.

Containerfile

@@ -1,6 +1,6 @@
 # Provide specific arg for setting the version of nodejs to use.
-# Should match what's in .nvmrc for development.
-ARG NODE_MAJOR_VERSION=18.20
+# Should match what's in flake.nix for development.
+ARG NODE_MAJOR_VERSION=20
 FROM docker.io/node:${NODE_MAJOR_VERSION}-alpine AS base
 # Install dependencies only when needed
 FROM base AS deps
@@ -9,8 +9,11 @@ RUN apk add --no-cache libc6-compat
 WORKDIR /app
 
 # Install dependencies
-COPY package.json package-lock.json pnpm-lock.yaml* ./
-RUN corepack enable pnpm && pnpm install  --frozen-lockfile
+COPY package.json package-lock.json ./
+# Right now the repo prefers `npm` rather than `pnpm`
+# COPY package.json pnpm-lock.yaml* ./
+# RUN corepack enable pnpm && pnpm install --frozen-lockfile
+RUN npm install --frozen-lockfile
 
 # Rebuild the source code only when needed
 FROM base AS builder

flake.nix

@@ -16,7 +16,8 @@
             file
             jq
             just
-            pnpm
+            # pnpm
+            nodejs_20
             postgresql
           ];
         };

justfile

@@ -3,8 +3,8 @@
 
 # run the app locally with live reload, via pnpm
 dev:
-  pnpm install
-  pnpm dev
+  npm install
+  npm run dev
 
 # build container image
 container: