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/security.mdc

@@ -0,0 +1,41 @@
+---
+description: Mandatory security checks, secret management, and security response protocol
+alwaysApply: true
+---
+
+# Security Guidelines
+
+## Mandatory Security Checks
+
+Before ANY commit:
+- [ ] No hardcoded secrets (API keys, passwords, tokens)
+- [ ] All user inputs validated
+- [ ] SQL injection prevention (parameterized queries)
+- [ ] XSS prevention (sanitized HTML)
+- [ ] CSRF protection enabled
+- [ ] Authentication/authorization verified
+- [ ] Rate limiting on all endpoints
+- [ ] Error messages don't leak sensitive data
+
+## Secret Management
+
+```typescript
+// NEVER: Hardcoded secrets
+const apiKey = "sk-proj-xxxxx"
+
+// ALWAYS: Environment variables
+const apiKey = process.env.OPENAI_API_KEY
+
+if (!apiKey) {
+  throw new Error('OPENAI_API_KEY not configured')
+}
+```
+
+## Security Response Protocol
+
+If security issue found:
+1. STOP immediately
+2. Use **security-reviewer** agent
+3. Fix CRITICAL issues before continuing
+4. Rotate any exposed secrets
+5. Review entire codebase for similar issues