build(docker): build frontend and server inside container; remove host build deps

docker/Dockerfile.prod

@@ -1,4 +1,21 @@
-FROM node:20-bullseye-slim
+######
+# Multi-stage production image that builds EVERYTHING inside containers
+######
+
+# ---------- Frontend builder ----------
+FROM node:20-bullseye-slim AS frontend-builder
+ENV npm_config_registry=https://registry.npmmirror.com
+WORKDIR /app
+
+# Install frontend deps and build (root project)
+COPY package.json ./
+COPY pnpm-lock.yaml ./
+RUN npm install --no-audit --no-fund
+COPY . .
+RUN npm run build
+
+# ---------- Server builder ----------
+FROM node:20-bullseye-slim AS server-builder
 ENV npm_config_registry=https://registry.npmmirror.com
 ENV npm_config_build_from_source=true
 
@@ -7,19 +24,31 @@ RUN apt-get update \
     && apt-get install -y --no-install-recommends python3 make g++ \
     && rm -rf /var/lib/apt/lists/*
 
+WORKDIR /app/server
+COPY server/package.json ./package.json
+RUN npm install --no-audit --no-fund --build-from-source
+COPY server/tsconfig.json ./tsconfig.json
+COPY server/src ./src
+RUN npm run build
+# Prune dev deps after build; keep native modules compiled for runtime
+RUN npm prune --omit=dev
+
+# ---------- Runtime ----------
+FROM node:20-bullseye-slim
+ENV npm_config_registry=https://registry.npmmirror.com
 WORKDIR /app
 
-# Install server deps in container (native modules match linux/amd64)
-COPY server/package.json ./server/package.json
-RUN cd server && npm install --omit=dev --build-from-source
-
-# Copy server runtime and prebuilt frontend from host
-COPY server/dist ./server/dist
-COPY dist ./frontend
-
 ENV PORT=3004
 ENV DB_PATH=/data/purchase.db
 
+# Server runtime
+COPY --from=server-builder /app/server/dist ./server/dist
+COPY --from=server-builder /app/server/node_modules ./server/node_modules
+COPY server/package.json ./server/package.json
+
+# Prebuilt frontend (from frontend-builder)
+COPY --from=frontend-builder /app/dist ./frontend
+
 EXPOSE 3004
 CMD ["node", "server/dist/index.js"]