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/internal/handler/ghost.go

@@ -0,0 +1,132 @@
+package handler
+
+import (
+	"net/http"
+	"time"
+
+	"sql-platform/config"
+	"sql-platform/internal/ghost"
+	"sql-platform/internal/model"
+
+	"github.com/gin-gonic/gin"
+)
+
+// POST /api/v1/ghost/dry-run
+func GhOstDryRun(c *gin.Context) {
+	var task ghost.GhOstTask
+	if err := c.ShouldBindJSON(&task); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"detail": err.Error()})
+		return
+	}
+	task.DryRun = true
+	task.Execute = false
+
+	result, err := ghost.RunGhOst(c.Request.Context(), task, config.C.GhOstPath)
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, result)
+		return
+	}
+	c.JSON(http.StatusOK, result)
+}
+
+// POST /api/v1/ghost/execute
+func GhOstExecute(c *gin.Context) {
+	var task ghost.GhOstTask
+	if err := c.ShouldBindJSON(&task); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"detail": err.Error()})
+		return
+	}
+	task.DryRun = false
+	task.Execute = true
+
+	taskID := ghost.RunGhOstAsync(task, config.C.GhOstPath, nil)
+	c.JSON(http.StatusAccepted, gin.H{
+		"task_id": taskID,
+		"message": "gh-ost execution started",
+	})
+}
+
+// GET /api/v1/ghost/status/:taskId
+func GhOstStatus(c *gin.Context) {
+	taskID := c.Param("taskId")
+	status, result := ghost.Manager.GetTaskStatus(taskID)
+	if status == "" {
+		c.JSON(http.StatusNotFound, gin.H{"detail": "Task not found"})
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{
+		"task_id": taskID,
+		"status":  status,
+		"result":  result,
+	})
+}
+
+// GET /api/v1/ghost/tasks
+func GhOstListTasks(c *gin.Context) {
+	tasks := ghost.Manager.ListTasks()
+	c.JSON(http.StatusOK, tasks)
+}
+
+// GET /api/v1/audit-rules
+func ListAuditRules(c *gin.Context) {
+	var rules []model.AuditRule
+	model.DB.Order("id").Find(&rules)
+	c.JSON(http.StatusOK, rules)
+}
+
+// GET /api/v1/announcements
+func ListAnnouncements(c *gin.Context) {
+	var announcements []model.Announcement
+	model.DB.Where("is_published = ?", true).Order("id DESC").Find(&announcements)
+	c.JSON(http.StatusOK, announcements)
+}
+
+// GET /api/v1/query-histories
+func ListQueryHistories(c *gin.Context) {
+	_, _, _ = c.GetInt("user_id"), c.GetString("username"), c.GetString("role")
+	
+	var histories []model.QueryHistory
+	model.DB.Order("id DESC").Limit(100).Find(&histories)
+	c.JSON(http.StatusOK, histories)
+}
+
+// GET /api/v1/settings
+func ListSettings(c *gin.Context) {
+	var settings []model.SystemSetting
+	model.DB.Order("sort_order").Find(&settings)
+	c.JSON(http.StatusOK, settings)
+}
+
+// GET /api/v1/notifications/channels
+func ListNotificationChannels(c *gin.Context) {
+	var channels []model.NotificationChannel
+	model.DB.Order("id").Find(&channels)
+	c.JSON(http.StatusOK, channels)
+}
+
+// GET /api/v1/notifications/templates
+func ListNotificationTemplates(c *gin.Context) {
+	var templates []model.NotificationTemplate
+	model.DB.Order("id").Find(&templates)
+	c.JSON(http.StatusOK, templates)
+}
+
+// GET /api/v1/workflows
+func ListWorkflows(c *gin.Context) {
+	var workflows []model.WorkflowDefinition
+	model.DB.Order("id").Find(&workflows)
+	c.JSON(http.StatusOK, workflows)
+}
+
+// GET /api/v1/instance-groups
+func ListInstanceGroups(c *gin.Context) {
+	var groups []model.InstanceGroup
+	model.DB.Order("id").Find(&groups)
+	c.JSON(http.StatusOK, groups)
+}
+
+// POST /api/v1/notifications/test
+func TestNotification(c *gin.Context) {
+	_ = time.Now()
+	c.JSON(http.StatusOK, gin.H{"message": "Notification sent (placeholder)"})
+}