🐛 fix(table-designer): 修复 DuckDB 表设计主键保存失效

- 为 DuckDB 表结构变更补充 ADD PRIMARY KEY 预览 SQL
- 保存前拦截已有主键表的主键替换与删除，避免假成功
- 补充 DuckDB 主键变更判定与 schema SQL 回归测试

frontend/src/components/tableDesignerDuckDbPrimaryKey.ts

@@ -0,0 +1,38 @@
+import type { EditableColumnSnapshot } from './tableDesignerSchemaSql';
+
+export interface DuckDbPrimaryKeyChangeSummary {
+  hasChange: boolean;
+  isAddingPrimaryKey: boolean;
+  isUnsupportedChange: boolean;
+}
+
+const collectPrimaryKeys = (columns: EditableColumnSnapshot[]): string[] => (
+  columns
+    .filter((column) => column.key === 'PRI')
+    .map((column) => String(column._key || '').trim())
+    .filter(Boolean)
+    .sort()
+);
+
+export const summarizeDuckDbPrimaryKeyChange = (
+  originalColumns: EditableColumnSnapshot[],
+  columns: EditableColumnSnapshot[],
+): DuckDbPrimaryKeyChangeSummary => {
+  const originalKeys = collectPrimaryKeys(originalColumns);
+  const nextKeys = collectPrimaryKeys(columns);
+  const hasChange = originalKeys.length !== nextKeys.length || originalKeys.some((key, index) => key !== nextKeys[index]);
+  if (!hasChange) {
+    return {
+      hasChange: false,
+      isAddingPrimaryKey: false,
+      isUnsupportedChange: false,
+    };
+  }
+
+  const isAddingPrimaryKey = originalKeys.length === 0 && nextKeys.length > 0;
+  return {
+    hasChange: true,
+    isAddingPrimaryKey,
+    isUnsupportedChange: !isAddingPrimaryKey,
+  };
+};