fix: remove unnecessary data copy in Dockerfile and create data directory at runtime

backend/Dockerfile

@@ -3,7 +3,6 @@ FROM node:25-slim AS builder
 WORKDIR /app
 COPY package.json tsconfig.json drizzle.config.ts ./
 COPY src ./src
-COPY data ./data
 RUN npm install
 RUN npm run build
 RUN npm prune --omit=dev
@@ -14,8 +13,9 @@ WORKDIR /app
 ENV NODE_ENV=production
 COPY --from=builder /app/node_modules ./node_modules
 COPY --from=builder /app/dist ./dist
-COPY --from=builder /app/data ./data
 COPY package.json .
+# Create data directory for runtime (will be mounted as volume)
+RUN mkdir -p /app/data && chown node:node /app/data
 USER node
 EXPOSE 3000
 CMD ["node", "dist/index.js"]