feat: Add complete user system implementation

- Create User, Role, Permission entities with their relationships
- Implement service interfaces and implementations for user system
- Add controllers for User, Role, Permission, UserRole, and RolePermission
- Include SQL schema files for the user system
- Document project structure in CLAUDE.md

This adds a complete RBAC (Role-Based Access Control) system with:
- User entity for managing user accounts
- Role entity for defining roles
- Permission entity for defining permissions
- UserRole entity for user-role relationships
- RolePermission entity for role-permission relationships

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -0,0 +1,66 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Build & Run Commands
+
+```bash
+# Build the project
+./mvnw clean package
+
+# Run the application
+./mvnw spring-boot:run
+
+# Run all tests
+./mvnw test
+
+# Run a single test class
+./mvnw test -Dtest=TestClassName
+
+# Run a single test method
+./mvnw test -Dtest=TestClassName#methodName
+```
+
+## Project Overview
+
+- **Framework**: Spring Boot 3.2.3 with Java 21
+- **ORM**: MyBatis Plus 3.5.5
+- **Database**: MySQL 8.0.33
+- **Cache**: Redis (Spring Data Redis)
+- **API Docs**: Swagger UI at `/swagger-ui.html`
+- **Auth**: JWT (jjwt 0.11.5)
+
+## Architecture
+
+Base package: `icu.sunway.ai_spring_example`
+
+This project follows a layered architecture with MyBatis Plus:
+
+| Layer | Location | Pattern |
+|-------|----------|---------|
+| Controller | `Controller/{EntityName}Controller/` | One subdirectory per entity |
+| Service | `Service/` | Interface `I{Name}Service` extends `IService<Entity>` |
+| Service Impl | `Service/Implements/` | `{Name}ServiceImpl` extends `ServiceImpl<Mapper, Entity>` |
+| Mapper | `Mapper/` | `{Name}Mapper` extends `BaseMapper<Entity>` |
+| Entity | `Entity/` | Lombok + MyBatis Plus annotations |
+| Config | `Config/` | CORS, Security, Redis, OpenAPI |
+| Utils | `Utils/` | Utility classes |
+
+## Key Utilities
+
+- **ResponseUtils**: Standard API responses - `ResponseUtils.success(data)` / `ResponseUtils.fail(message)`
+- **PageUtils**: Pagination - `PageUtils.createPage(page, limit)` returns `Page<T>` for MyBatis Plus
+- **RedisUtils**: Redis operations (inject with `@Resource`)
+- **JsonUtils**: JSON serialization - `JsonUtils.toJson()` / `JsonUtils.toObject()`
+- **ValidationUtils**: Input validation (email, phone, URL, IP, password strength, etc.)
+
+## Configuration
+
+- Copy `application-example.yaml` to `application.yaml` and fill in database/Redis credentials
+- `application.yaml` is gitignored (contains sensitive data)
+- Uses dynamic multi-datasource (primary datasource named "master")
+
+## Security Notes
+
+- Current `SecurityConfig` is permissive (all requests allowed) - configure for production
+- Stateless session management configured for JWT authentication