Add new skills for backend patterns, coding standards, continuous learning, and NestJS best practices

- Introduced backend patterns skill with guidelines on API design, database optimization, and server-side best practices.
- Added coding standards skill outlining universal coding principles for TypeScript, NestJS, and Node.js development.
- Implemented continuous learning skill to automatically extract reusable patterns from Cursor sessions.
- Created NestJS best practices skill detailing architecture patterns, dependency injection, error handling, and security measures.
- Included various rules and templates for NestJS best practices to ensure production-ready applications.

.cursor/rules/nestjs.mdc

@@ -0,0 +1,28 @@
+---
+description: NestJS modular TDD structure with Drizzle and PostgreSQL
+globs: "**/*.{ts,js}"
+alwaysApply: false
+---
+
+# NestJS Project Conventions
+
+Stack: NestJS + PostgreSQL + Drizzle ORM. Follow `.agents/skills/nestjs-best-practices` and `.agents/skills/project-guidelines-example`.
+
+## Modules
+
+- One feature folder under `src/modules/`
+- Each feature has `*.module.ts`, `*.controller.ts`, `*.service.ts`, `dto/`
+- Share cross-cutting code via `src/common/` (filters, guards, pipes, interceptors)
+
+## Tests
+
+- Unit tests colocated as `*.spec.ts`
+- E2E tests in `test/*.e2e-spec.ts` with Supertest
+- Write tests first (RED → GREEN → REFACTOR)
+- Mock Drizzle and external services, not Nest internals
+
+## Database
+
+- Schema and SQL migrations in `drizzle/`
+- Config in `drizzle.config.ts`
+- Never mutate production schema without a migration