🐛 fix(metadata): 修复 Oracle 字段元数据显示缺失

- Oracle 元数据查询为字段名、类型、默认值、注释等列补齐稳定别名

- 新增字段定义归一化工具，兼容 name/Name/COLUMN_NAME 等返回形态

- 修复 DataGrid、DataViewer、QueryEditor、TableDesigner 对字段元数据的读取

- 补充 Oracle 字段注释、表头元数据和主键定位回归测试

frontend/src/utils/columnDefinition.ts

@@ -0,0 +1,59 @@
+import type { ColumnDefinition } from '../types';
+
+const readStringProperty = (value: unknown, keys: string[]): string => {
+  const source = value as Record<string, unknown> | null | undefined;
+  if (!source || typeof source !== 'object') return '';
+
+  for (const key of keys) {
+    const raw = source[key];
+    if (raw !== undefined && raw !== null) {
+      return String(raw).trim();
+    }
+  }
+
+  for (const [sourceKey, raw] of Object.entries(source)) {
+    if (keys.some((key) => sourceKey.toLowerCase() === key.toLowerCase())) {
+      return raw === undefined || raw === null ? '' : String(raw).trim();
+    }
+  }
+
+  return '';
+};
+
+export const getColumnDefinitionName = (column: unknown): string => (
+  readStringProperty(column, ['name', 'Name', 'COLUMN_NAME', 'column_name', 'field', 'Field'])
+);
+
+export const getColumnDefinitionType = (column: unknown): string => (
+  readStringProperty(column, ['type', 'Type', 'DATA_TYPE', 'data_type'])
+);
+
+export const getColumnDefinitionKey = (column: unknown): string => (
+  readStringProperty(column, ['key', 'Key', 'COLUMN_KEY', 'column_key'])
+);
+
+export const getColumnDefinitionExtra = (column: unknown): string => (
+  readStringProperty(column, ['extra', 'Extra'])
+);
+
+export const getColumnDefinitionComment = (column: unknown): string => (
+  readStringProperty(column, ['comment', 'Comment', 'COMMENTS', 'comments', 'COLUMN_COMMENT', 'column_comment'])
+);
+
+export const normalizeColumnDefinition = (column: unknown): ColumnDefinition => {
+  const source = (column && typeof column === 'object' ? column : {}) as Partial<ColumnDefinition>;
+  return {
+    ...source,
+    name: getColumnDefinitionName(column),
+    type: getColumnDefinitionType(column),
+    nullable: readStringProperty(column, ['nullable', 'Nullable', 'NULLABLE', 'is_nullable']),
+    key: getColumnDefinitionKey(column),
+    default: source.default,
+    extra: getColumnDefinitionExtra(column),
+    comment: getColumnDefinitionComment(column),
+  };
+};
+
+export const normalizeColumnDefinitions = (columns: unknown): ColumnDefinition[] => (
+  Array.isArray(columns) ? columns.map(normalizeColumnDefinition) : []
+);