feat: Go后端LDAP真实对接 — AES-256-GCM密码加解密 + 登录LDAP fallback

- 新增 crypto.go: AES-256-GCM 加解密，与 Python backend 兼容
- auth.go: Login 添加 LDAP fallback（本地优先→LDAP绑定→自动创建本地用户）
- ldap.go: 实现真实 LDAP 连接/用户搜索/密码验证/OU列表/用户列表
- 所有 LDAP 操作解密 admin_password 后使用
- 新增/更新密码存储时加密
- router.go: 补充 delete-user 路由
- 添加 go-ldap/v3 依赖

backend/internal/handler/instance_detail.go

@@ -0,0 +1,132 @@
+package handler
+
+import (
+	"net/http"
+
+	"sql-platform/internal/model"
+
+	"github.com/gin-gonic/gin"
+)
+
+// GET /api/v1/instances/:id/detail/databases
+func DetailListDatabases(c *gin.Context) {
+	id := c.Param("id")
+	var instance model.Instance
+	if err := model.DB.First(&instance, id).Error; err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"detail": "Instance not found"})
+		return
+	}
+	// TODO: actual SHOW DATABASES
+	c.JSON(http.StatusOK, []string{"information_schema"})
+}
+
+// GET /api/v1/instances/:id/detail/tables
+func DetailListTables(c *gin.Context) {
+	id := c.Param("id")
+	dbName := c.Query("database")
+	var instance model.Instance
+	if err := model.DB.First(&instance, id).Error; err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"detail": "Instance not found"})
+		return
+	}
+	// TODO: actual SHOW TABLES from database
+	_ = dbName
+	c.JSON(http.StatusOK, []interface{}{})
+}
+
+// GET /api/v1/instances/:id/detail/db-schema
+func DetailDbSchema(c *gin.Context) {
+	id := c.Param("id")
+	dbName := c.Query("database")
+	var instance model.Instance
+	if err := model.DB.First(&instance, id).Error; err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"detail": "Instance not found"})
+		return
+	}
+	// TODO: actual schema introspection
+	_ = dbName
+	c.JSON(http.StatusOK, map[string]interface{}{})
+}
+
+// GET /api/v1/instances/:id/detail/table-detail
+func DetailTableDetail(c *gin.Context) {
+	id := c.Param("id")
+	dbName := c.Query("database")
+	tableName := c.Query("table")
+	var instance model.Instance
+	if err := model.DB.First(&instance, id).Error; err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"detail": "Instance not found"})
+		return
+	}
+	// TODO: actual SHOW CREATE TABLE + SHOW COLUMNS + SHOW INDEX
+	_, _ = dbName, tableName
+	c.JSON(http.StatusOK, gin.H{
+		"ddl":     "",
+		"columns": []interface{}{},
+		"indexes": []interface{}{},
+	})
+}
+
+// GET /api/v1/instances/:id/detail/processlist
+func DetailProcesslist(c *gin.Context) {
+	id := c.Param("id")
+	var instance model.Instance
+	if err := model.DB.First(&instance, id).Error; err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"detail": "Instance not found"})
+		return
+	}
+	// TODO: actual SHOW PROCESSLIST
+	c.JSON(http.StatusOK, []interface{}{})
+}
+
+// GET /api/v1/instances/:id/detail/status
+func DetailStatus(c *gin.Context) {
+	id := c.Param("id")
+	var instance model.Instance
+	if err := model.DB.First(&instance, id).Error; err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"detail": "Instance not found"})
+		return
+	}
+	// TODO: actual SHOW GLOBAL STATUS
+	c.JSON(http.StatusOK, gin.H{
+		"key_metrics": map[string]string{},
+		"all_status":  []interface{}{},
+	})
+}
+
+// POST /api/v1/instances/:id/detail/processlist/:pid/kill
+func DetailKillProcess(c *gin.Context) {
+	c.JSON(http.StatusOK, gin.H{"message": "Process killed (placeholder)"})
+}
+
+// GET /api/v1/instances/:id/detail/users
+func DetailListUsers(c *gin.Context) {
+	id := c.Param("id")
+	var instance model.Instance
+	if err := model.DB.First(&instance, id).Error; err != nil {
+		c.JSON(http.StatusNotFound, gin.H{"detail": "Instance not found"})
+		return
+	}
+	// TODO: actual SELECT from mysql.user
+	c.JSON(http.StatusOK, []interface{}{})
+}
+
+// POST /api/v1/query/execute
+func ExecuteQuery(c *gin.Context) {
+	var input struct {
+		InstanceID int    `json:"instance_id"`
+		Database   string `json:"database"`
+		SQL        string `json:"sql"`
+	}
+	if err := c.ShouldBindJSON(&input); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"detail": err.Error()})
+		return
+	}
+	// TODO: actual SQL execution
+	c.JSON(http.StatusOK, gin.H{
+		"columns": []interface{}{},
+		"rows":    []interface{}{},
+		"total":   0,
+		"cost_ms": 0,
+	})
+}