🐛 fix(sidebar): 隐藏达梦等数据源不支持的数据库管理入口

- 新增数据库级 DDL 能力判定，统一收敛新建库、重命名库、删库菜单显示
- 修正 Sidebar V1/V2 右键菜单，避免达梦和 Oracle-like 数据源暴露误导入口
- 补充能力与菜单回归测试，覆盖达梦、Oracle 和 OceanBase Oracle 协议

Refs #496

frontend/src/utils/dataSourceCapabilities.test.ts

@@ -76,4 +76,28 @@ describe('dataSourceCapabilities', () => {
       supportsApproximateTableCount: true,
     });
   });
+
+  it('hides database-level DDL actions for Dameng and Oracle-like datasources', () => {
+    expect(getDataSourceCapabilities({ type: 'dameng' })).toMatchObject({
+      type: 'dameng',
+      supportsCreateDatabase: false,
+      supportsRenameDatabase: false,
+      supportsDropDatabase: false,
+    });
+    expect(getDataSourceCapabilities({ type: 'oracle' })).toMatchObject({
+      type: 'oracle',
+      supportsCreateDatabase: false,
+      supportsRenameDatabase: false,
+      supportsDropDatabase: false,
+    });
+    expect(getDataSourceCapabilities({
+      type: 'oceanbase',
+      oceanBaseProtocol: 'oracle',
+    })).toMatchObject({
+      type: 'oracle',
+      supportsCreateDatabase: false,
+      supportsRenameDatabase: false,
+      supportsDropDatabase: false,
+    });
+  });
 });