chore: 添加 prisma 编译文件到 .gitignore

防止 seed.ts 的编译产物（.js, .js.map, .d.ts）被误提交。
seed.ts 应该保持为源码形式，由 ts-node 直接执行。

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

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

backend/services/referral-service/.gitignore

@@ -4,6 +4,11 @@ node_modules/
 # Build output
 dist/
 
+# Prisma compiled files (seed.ts should not be compiled)
+prisma/*.js
+prisma/*.js.map
+prisma/*.d.ts
+
 # Coverage
 coverage/