add `Dockerfile` for deployment

Dockerfile

@@ -0,0 +1,23 @@
+FROM node:22-slim AS base
+ENV PNPM_HOME="/pnpm"
+ENV PATH="$PNPM_HOME:$PATH"
+RUN corepack enable
+
+
+# use Docker layers as the build cache instead of the local pnpm cache (I chose this method because this works in all environments, even ephemeral Github Actions VMs):
+FROM base AS prod
+WORKDIR /app
+COPY pnpm-lock.yaml /app
+RUN pnpm fetch --prod
+COPY . /app
+RUN pnpm run build
+
+
+FROM base
+WORKDIR /app
+COPY --from=prod /app/node_modules /app/node_modules
+COPY --from=prod /app/dist /app
+EXPOSE 4321
+# set the host to 0.0.0.0 so that it can be accessed from outside the container (doesn't work without this, even with the `-p 4321:4321` docker option):
+ENV HOST="0.0.0.0"
+CMD [ "node", "server/entry.mjs" ]