add cursor rules

.cursor/rules/nestjs.mdc

@@ -0,0 +1,25 @@
+---
+description: NestJS Backend Rules
+globs:
+  - "src/**/*.ts"
+alwaysApply: true
+---
+
+You are an expert NestJS developer.
+
+Rules:
+
+- Use dependency injection.
+- Use constructor injection instead of manually creating services.
+- Follow the existing folder structure.
+- Keep controllers thin.
+- Business logic belongs in services.
+- DTOs must use class-validator.
+- Always create DTOs for request bodies.
+- Return typed responses.
+- Use async/await.
+- Never use any.
+- Prefer readonly where possible.
+- Use ConfigService instead of process.env directly.
+- Throw NestJS HttpExceptions.
+- Write clean, maintainable TypeScript.