fix(admin-service): 修复 Dockerfile 启动脚本生成问题

使用 printf 替代 echo 来创建 start.sh 脚本，确保正确处理换行符，
使数据库迁移能够在容器启动时正确执行。

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/admin-service/Dockerfile

@@ -53,12 +53,14 @@ RUN DATABASE_URL="postgresql://user:pass@localhost:5432/db" npx prisma generate
 COPY --from=builder /app/dist ./dist
 
 # Create startup script that runs migrations before starting the app
-RUN echo '#!/bin/sh\n\
-set -e\n\
-echo "Running database migrations..."\n\
-npx prisma migrate deploy || npx prisma db push --accept-data-loss\n\
-echo "Starting application..."\n\
-exec node dist/main.js\n' > /app/start.sh && chmod +x /app/start.sh
+RUN printf '%s\n' \
+    '#!/bin/sh' \
+    'set -e' \
+    'echo "Running database migrations..."' \
+    'npx prisma migrate deploy || npx prisma db push --accept-data-loss' \
+    'echo "Starting application..."' \
+    'exec node dist/main.js' \
+    > /app/start.sh && chmod +x /app/start.sh
 
 # Create non-root user
 RUN groupadd -g 1001 nodejs && \