feat: v0.3.1 — Go/Gin 后端重写 + gh-ost 集成

架构变更:
- Python/FastAPI → Go/Gin 重写（Python 后端保留在 backend-python/）
- GORM + SQLite（兼容现有数据库表结构）
- JWT 认证 + RBAC 权限中间件

Go 后端结构:
- cmd/server/main.go — 入口，端口 9000
- config/config.go — 环境变量配置
- internal/model/ — GORM 模型（30张表，完全兼容 SQLite）
- internal/handler/ — auth/instance/ticket/dashboard/ghost handler
- internal/middleware/ — JWT 认证 + CORS
- internal/ghost/ — gh-ost 集成模块（同步/异步执行，任务管理）
- router/router.go — API 路由注册（/api/v1/...）

gh-ost 集成:
- RunGhOst() 同步执行
- RunGhOstAsync() 异步执行 + 进度追踪
- TaskManager 管理多个并发任务
- API: POST /ghost/dry-run, /ghost/execute, GET /ghost/status/:taskId

核心 API 已对齐:
- POST /auth/login (JWT)
- GET /dashboard/stats, /dashboard/my-tickets
- GET /tickets/statistics, CRUD + approve/execute
- GET/POST/PUT/DELETE /instances
- GET /users, /audit-rules, /announcements, /settings

已验证:
- 登录 admin/admin123 ✅
- Dashboard 99工单/110查询/4实例 ✅
- 工单统计按角色过滤 ✅

backend/cmd/server/main.go

@@ -0,0 +1,81 @@
+package main
+
+import (
+	"fmt"
+	"log"
+
+	"sql-platform/config"
+	"sql-platform/internal/middleware"
+	"sql-platform/internal/model"
+	"sql-platform/router"
+
+	"github.com/gin-gonic/gin"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+)
+
+func main() {
+	// Load config
+	config.Init()
+
+	if !config.C.Debug {
+		gin.SetMode(gin.ReleaseMode)
+	}
+
+	// Connect to SQLite
+	db, err := gorm.Open(sqlite.Open(config.C.DBPath), &gorm.Config{})
+	if err != nil {
+		log.Fatalf("Failed to connect to database: %v", err)
+	}
+	model.DB = db
+
+	// Auto-migrate (add missing tables/columns, won\'t drop existing data)
+	_ = db.AutoMigrate(
+		&model.User{},
+		&model.Instance{},
+		&model.Ticket{},
+		&model.TicketApproval{},
+		&model.TicketSQLItem{},
+		&model.AuditRule{},
+		&model.AuditLog{},
+		&model.QueryHistory{},
+		&model.WorkflowDefinition{},
+		&model.WorkflowStep{},
+		&model.WorkflowVersion{},
+		&model.WorkflowExecutionLog{},
+		&model.Announcement{},
+		&model.InstanceGroup{},
+		&model.InstanceGroupMember{},
+		&model.LDAPConfig{},
+		&model.NotificationChannel{},
+		&model.NotificationTemplate{},
+		&model.SystemSetting{},
+		&model.OperationLog{},
+		&model.MaskingRule{},
+		&model.Backup{},
+		&model.SchemaRevision{},
+		&model.SlowLog{},
+		&model.ScheduledTask{},
+		&model.ScheduledTaskLog{},
+		&model.UserGroup{},
+	)
+
+	// Setup Gin
+	r := gin.Default()
+	r.Use(middleware.CORSMiddleware())
+
+	// Health check
+	r.GET("/health", func(c *gin.Context) {
+		c.JSON(200, gin.H{"status": "ok", "version": "0.3.1", "backend": "go"})
+	})
+
+	// Routes
+	router.Setup(r)
+
+	// Start server
+	addr := fmt.Sprintf(":%s", config.C.Port)
+	log.Printf("SQL Platform Go backend starting on %s", addr)
+	if err := r.Run(addr); err != nil {
+		log.Fatalf("Failed to start server: %v", err)
+	}
+}