fix: SHOW TABLE STATUS 列名小写化修复前端 key 警告 + table-detail 400 错误

根因: Go 后端 DetailListTables 返回 SHOW TABLE STATUS 原始列名(如 Name, Engine, Rows)
前端 TableMeta 使用小写 key(name, engine, rows), 导致 t.name = undefined
结果: key 警告 + handleExpandTable(dbName, undefined) 触发 table-detail 400

修复: instance_detail.go 中 DetailListTables 将列名统一 strings.ToLower()

backend/internal/handler/instance_detail.go

@@ -105,14 +105,15 @@ func DetailListTables(c *gin.Context) {
 			ptrValues[i] = &values[i]
 		}
 		rows.Scan(ptrValues...)
+		// Normalize to lowercase keys for frontend compatibility
 		rowMap := make(map[string]interface{})
 		for i, col := range cols {
 			val := values[i]
 			b, ok := val.([]byte)
 			if ok {
-				rowMap[col] = string(b)
+				rowMap[strings.ToLower(col)] = string(b)
 			} else {
-				rowMap[col] = val
+				rowMap[strings.ToLower(col)] = val
 			}
 		}
 		tables = append(tables, rowMap)