feat: Enhance security and validation in backend

- Added helmet for security headers and configured content security policy
- Implemented CORS with a whitelist for allowed origins
- Introduced express-validator for input validation in API endpoints
- Set request size limits to prevent DoS attacks
- Added global error handling and 404 response
- Updated TypeScript configuration to use node16 module resolution
- Improved Docker Compose configuration for security and resource limits
- Created a comprehensive .env.example for environment configuration
- Implemented automated security scans in CI/CD with Trivy
- Added cleanup script for debugging ports
- Established a detailed security policy document

backend/tsconfig.json

@@ -1,7 +1,7 @@
 {
   "compilerOptions": {
     "target": "ES2020",
-    "module": "commonjs",
+    "module": "node16",
     "lib": ["ES2020"],
     "outDir": "./dist",
     "rootDir": "./src",
@@ -20,7 +20,7 @@
     "noImplicitThis": true,
     "noImplicitReturns": true,
     "noFallthroughCasesInSwitch": true,
-    "moduleResolution": "node",
+    "moduleResolution": "node16",
     "allowSyntheticDefaultImports": true,
     "experimentalDecorators": true,
     "emitDecoratorMetadata": true