feat(shared): add error handling & structured logging strategy

- Global exception filter with consistent error response format
- Domain exceptions (NotFoundException, ValidationException, etc.)
- Error codes enum for domain-specific error identification
- Correlation ID middleware for request tracing
- Request/response logging middleware with structured JSON
- PII masking in logs (emails, phone numbers, sensitive fields)
- Enhanced LoggerService with pino formatters and ISO timestamps
- Tests for exception filter, domain exceptions, and PII masker

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/modules/shared/domain/error-codes.ts

@@ -0,0 +1,36 @@
+/**
+ * Domain-specific error codes for consistent error identification across the platform.
+ * Format: DOMAIN_ACTION_REASON
+ */
+export enum ErrorCode {
+  // General
+  INTERNAL_ERROR = 'INTERNAL_ERROR',
+  VALIDATION_FAILED = 'VALIDATION_FAILED',
+  NOT_FOUND = 'NOT_FOUND',
+  CONFLICT = 'CONFLICT',
+  UNAUTHORIZED = 'UNAUTHORIZED',
+  FORBIDDEN = 'FORBIDDEN',
+  BAD_REQUEST = 'BAD_REQUEST',
+  TOO_MANY_REQUESTS = 'TOO_MANY_REQUESTS',
+
+  // Auth
+  AUTH_INVALID_CREDENTIALS = 'AUTH_INVALID_CREDENTIALS',
+  AUTH_TOKEN_EXPIRED = 'AUTH_TOKEN_EXPIRED',
+  AUTH_TOKEN_INVALID = 'AUTH_TOKEN_INVALID',
+  AUTH_INSUFFICIENT_PERMISSIONS = 'AUTH_INSUFFICIENT_PERMISSIONS',
+
+  // User
+  USER_NOT_FOUND = 'USER_NOT_FOUND',
+  USER_ALREADY_EXISTS = 'USER_ALREADY_EXISTS',
+  USER_INVALID_PHONE = 'USER_INVALID_PHONE',
+
+  // Course
+  COURSE_NOT_FOUND = 'COURSE_NOT_FOUND',
+  COURSE_ALREADY_PUBLISHED = 'COURSE_ALREADY_PUBLISHED',
+  COURSE_ENROLLMENT_CLOSED = 'COURSE_ENROLLMENT_CLOSED',
+
+  // Payment
+  PAYMENT_FAILED = 'PAYMENT_FAILED',
+  PAYMENT_ALREADY_PROCESSED = 'PAYMENT_ALREADY_PROCESSED',
+  PAYMENT_INVALID_AMOUNT = 'PAYMENT_INVALID_AMOUNT',
+}