Change aftersales serial to YYMMNN monthly sequence

User-requested format: zjbf-sh-260501 (26=year, 05=month, 01=monthly seq).
Sequence resets each month and skips soft-deleted entries to avoid reuse.
Also documents aftersales API and new technician role in AGENTS.md / README.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

AGENTS.md

@@ -44,6 +44,7 @@ backend-go/
 ├── config/                  # Configuration management
 │   └── config.go            # Config loading (.env, config.yaml, env vars)
 ├── controllers/             # HTTP request handlers
+│   ├── aftersales_controller.go # Aftersales orders: create, query, submit, confirm, qrcode
 │   ├── auth_controller.go   # Auth: login, profile, password change
 │   ├── companies_controller.go  # Company CRUD
 │   ├── employees_controller.go  # Employee serials: generate, query, update, revoke, qrcode
@@ -55,12 +56,13 @@ backend-go/
 ├── logger/                  # Structured logging
 │   └── logger.go            # Zap logger wrapper
 ├── middleware/              # Middleware
-│   └── auth.go              # JWT auth, Admin permission check
+│   └── auth.go              # JWT auth, Admin / Technician permission checks
 ├── models/                  # Data models and DTOs
-│   └── models.go            # User, Company, Serial, EmployeeSerial and DTOs
+│   └── models.go            # User, Company, Serial, EmployeeSerial, AftersalesOrder and DTOs
 ├── routes/                  # Route configuration
 │   └── routes.go            # API route registration
 ├── services/                # Business logic layer
+│   ├── aftersales_service.go # Aftersales orders: create, list, update, submit, customer confirm, qrcode
 │   ├── 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
@@ -87,6 +89,9 @@ backend-go/
 - **Serials**: `POST /api/serials/generate`, `POST /api/serials/generate-with-prefix`, `POST /api/serials/:serialNumber/qrcode`, `GET /api/serials/:serialNumber/query`, `GET /api/serials`, `PATCH /api/serials/:serialNumber`, `PUT /api/serials/:serialNumber`, `POST /api/serials/:serialNumber/revoke`
 - **Companies**: `GET /api/companies/stats/overview`, `GET /api/companies`, `GET /api/companies/:companyName`, `POST /api/companies`, `PATCH /api/companies/:companyName`, `PUT /api/companies/:companyName`, `POST /api/companies/:companyName/revoke`, `DELETE /api/companies/:companyName/serials/:serialNumber`, `DELETE /api/companies/:companyName`
 - **Employee Serials**: `POST /api/employee-serials/generate`, `POST /api/employee-serials/:serialNumber/qrcode`, `GET /api/employee-serials/:serialNumber/query`, `GET /api/employee-serials`, `PATCH /api/employee-serials/:serialNumber`, `PUT /api/employee-serials/:serialNumber`, `POST /api/employee-serials/:serialNumber/revoke`
+- **Aftersales** (公开): `GET /api/aftersales/:serialNumber/query`, `POST /api/aftersales/:serialNumber/confirm`
+- **Aftersales** (技术员+管理员): `POST /api/aftersales`, `GET /api/aftersales`, `GET /api/aftersales/:serialNumber`, `PATCH /api/aftersales/:serialNumber`, `POST /api/aftersales/:serialNumber/qrcode`, `POST /api/aftersales/:serialNumber/submit`
+- **Aftersales** (仅管理员): `POST /api/aftersales/:serialNumber/reassign`, `POST /api/aftersales/:serialNumber/force-close`, `DELETE /api/aftersales/:serialNumber`
 
 ### Import Organization
 Standard imports followed by third-party imports, then project imports (sorted alphabetically):
@@ -219,6 +224,7 @@ After modifying Swagger annotations, run `make swagger`.
 ### Middleware
 - **JWTAuthMiddleware**: Validates JWT tokens, sets user in context
 - **AdminMiddleware**: Checks if user has admin role
+- **TechnicianMiddleware**: Allows admin and technician roles (used for aftersales endpoints)
 - Access current user: `user, ok := GetCurrentUser(ctx)`
 
 ### Git Hooks