build(docker): add multi-stage production Dockerfile with health check

Dockerfile

@@ -1,13 +1,37 @@
-FROM node:22-alpine
+# Multi-stage production Dockerfile for gameno-api
+
+# ------------------------------------------------------------------------------
+# Stage 1: Install production dependencies
+# ------------------------------------------------------------------------------
+FROM node:22-alpine AS dependencies
 
 WORKDIR /app
 
 COPY package*.json ./
 
-RUN npm install
+RUN npm ci --omit=dev && npm cache clean --force
 
-COPY . .
+# ------------------------------------------------------------------------------
+# Stage 2: Production runtime image
+# ------------------------------------------------------------------------------
+FROM node:22-alpine AS production
+
+WORKDIR /app
+
+ENV NODE_ENV=production \
+    PORT=3000
+
+# Copy installed production dependencies and application code with proper ownership
+COPY --chown=node:node --from=dependencies /app/node_modules ./node_modules
+COPY --chown=node:node . .
+
+# Run as non-root user
+USER node
 
 EXPOSE 3000
 
-CMD ["npm", "start"]
+# Healthcheck targeting the API health endpoint
+HEALTHCHECK --interval=30s --timeout=5s --start-period=15s --retries=3 \
+  CMD wget --no-verbose --tries=1 --spider http://localhost:3000/api/health || exit 1
+
+CMD ["node", "app.js"]