feat: Redis查询结果优化 — 复制按钮+JSON自动格式化+语义化列名

1. GET/HGET/TTL等单值命令: columns改为[key,value]替代[command,result]
2. DBSIZE等无key命令保持[command,result]格式
3. 前端添加复制按钮(Clipboard API), 2秒反馈
4. JSON值自动检测并格式化显示(whitespace-pre-wrap)
5. 结果区最大高度350px→500px
6. cost_ms字段兼容处理

backend/internal/handler/instance_detail.go

@@ -702,11 +702,25 @@ func executeRedisQuery(instance *model.Instance, dbSelect string, command string
 			}
 			columns = []string{"field", "value"}
 		} else {
-			rows = append(rows, map[string]interface{}{
-				"command": command,
-				"result":  fmt.Sprintf("%v", v),
-			})
-			columns = []string{"command", "result"}
+			// Single value result (GET, HGET, TYPE, TTL, etc.)
+			// Try to extract key name from command
+			keyName := ""
+			if len(parts) > 1 {
+				keyName = parts[1]
+			}
+			if keyName != "" {
+				rows = append(rows, map[string]interface{}{
+					"key":   keyName,
+					"value": fmt.Sprintf("%v", v),
+				})
+				columns = []string{"key", "value"}
+			} else {
+				rows = append(rows, map[string]interface{}{
+					"command": command,
+					"result":  fmt.Sprintf("%v", v),
+				})
+				columns = []string{"command", "result"}
+			}
 		}
 	}