Add employee code assignment function

AGENTS.md

@@ -38,12 +38,51 @@ swag init -g main.go     # Alternative command
 
 ## Code Style Guidelines
 
+## Code Style Guidelines
+
 ### Project Structure
-- **controllers/**: HTTP request handlers, use helper functions (GetCurrentUser, BindJSON, ErrorResponse, SuccessResponse)
-- **services/**: Business logic layer, return errors to controllers
-- **models/**: Data models with JSON and GORM tags, DTOs for API
-- **middleware/**: JWT authentication and admin role checks
-- **database/**: SQLite/PostgreSQL connection and migrations
+```
+backend-go/
+├── config/                  # Configuration management
+│   └── config.go            # Config loading (.env, config.yaml, env vars)
+├── controllers/             # HTTP request handlers
+│   ├── auth_controller.go   # Auth: login, profile, password change
+│   ├── companies_controller.go  # Company CRUD
+│   ├── employees_controller.go  # Employee serials: generate, query, update, revoke, qrcode
+│   ├── helper.go            # Helper functions (GetCurrentUser, BindJSON, Response)
+│   └── serials_controller.go    # Company serials: generate, query, update, revoke, qrcode
+├── database/                # Database connection and migrations
+│   └── database.go          # GORM init, AutoMigrate
+├── docs/                    # Swagger documentation (auto-generated)
+├── logger/                  # Structured logging
+│   └── logger.go            # Zap logger wrapper
+├── middleware/              # Middleware
+│   └── auth.go              # JWT auth, Admin permission check
+├── models/                  # Data models and DTOs
+│   └── models.go            # User, Company, Serial, EmployeeSerial and DTOs
+├── routes/                  # Route configuration
+│   └── routes.go            # API route registration
+├── services/                # Business logic layer
+│   ├── auth_service.go      # Auth: validate user, generate token, password management
+│   ├── companies_service.go # Company CRUD
+│   ├── employees_service.go # Employee serials: generate, query, update, revoke, qrcode
+│   ├── serials_service.go   # Company serials: generate, query, update, revoke, qrcode
+│   └── services_test.go     # Unit tests
+├── tests/                   # Integration tests
+│   └── main_test.go         # End-to-end tests
+├── data/                    # SQLite data directory
+├── main.go                  # Application entry point
+├── go.mod                   # Go dependencies
+├── Makefile                 # Build tasks
+└── .env.example             # Environment variable example
+```
+
+### Layer Responsibilities
+- **controllers/**: Receive HTTP requests, validate params, call services, return responses
+- **services/**: Business logic, data processing, database interaction, return results or errors
+- **models/**: Data structure definitions, GORM models, API request/response DTOs
+- **middleware/**: Authentication and authorization
+- **routes/**: Route registration, connect controllers to router
 
 ### Import Organization
 Standard imports followed by third-party imports, then project imports (sorted alphabetically):
@@ -61,8 +100,8 @@ import (
 ```
 
 ### Naming Conventions
-- **Controllers**: `AuthController`, `SerialsController`, `CompaniesController`
-- **Services**: `AuthService`, `SerialsService`, `CompaniesService`
+- **Controllers**: `AuthController`, `SerialsController`, `CompaniesController`, `EmployeeSerialsController`
+- **Services**: `AuthService`, `SerialsService`, `CompaniesService`, `EmployeeSerialsService`
 - **Models**: `User`, `Company`, `Serial` (use PascalCase for exported structs)
 - **DTOs**: `LoginDTO`, `ChangePasswordDTO`, `UpdateProfileDTO` (DTO suffix)
 - **Functions**: `ValidateUser`, `Generate`, `Query` (PascalCase for exported)