🐛 fix(data-import): 约束导入目标下拉框宽度 (#774)

- 限制连接、数据库和目标表选择器不超出目标卡片
- 保留长名称单行省略并适配单双列布局
- 新增目标选择器宽度约束回归测试

frontend/src/components/DataImportWorkbench.test.tsx

@@ -177,6 +177,20 @@ describe('DataImportWorkbench', () => {
     expect(mocks.dbGetTables).toHaveBeenCalledWith(expect.anything(), 'app');
   });
 
+  it('keeps every target selector within the import target card', async () => {
+    const renderer = await renderWorkbench();
+
+    ['connection', 'database', 'table'].forEach((field) => {
+      expect(renderer.root.findByProps({
+        'data-import-target-field': field,
+      }).props.style).toEqual({
+        width: '100%',
+        minWidth: 0,
+        maxWidth: '100%',
+      });
+    });
+  });
+
   it('filters every SQL import protection from database mode connections', async () => {
     const primaryConnection = mocks.storeState.connections[0];
     mocks.storeState.connections = [

frontend/src/components/DataImportWorkbench.tsx

@@ -33,6 +33,12 @@ import './DataImportWorkbench.css';
 
 const { Text, Title } = Typography;
 
+const targetSelectStyle: React.CSSProperties = {
+  width: '100%',
+  minWidth: 0,
+  maxWidth: '100%',
+};
+
 type SelectOption = {
   value: string;
   label: React.ReactNode;
@@ -520,6 +526,7 @@ const DataImportWorkbench: React.FC<{ tab: TabData }> = ({ tab }) => {
               <Text type="secondary">{t('data_import.workbench.label.connection')}</Text>
               <Select
                 data-import-target-field="connection"
+                style={targetSelectStyle}
                 value={selectedConnectionId || undefined}
                 options={connectionOptions}
                 placeholder={t('data_import.workbench.placeholder.select_connection')}
@@ -538,6 +545,7 @@ const DataImportWorkbench: React.FC<{ tab: TabData }> = ({ tab }) => {
               </Text>
               <Select
                 data-import-target-field="database"
+                style={targetSelectStyle}
                 value={selectedDbName || undefined}
                 options={databaseOptions}
                 placeholder={loadingDatabases
@@ -559,6 +567,7 @@ const DataImportWorkbench: React.FC<{ tab: TabData }> = ({ tab }) => {
                 <Text type="secondary">{t('data_import.workbench.label.table')}</Text>
                 <Select
                   data-import-target-field="table"
+                  style={targetSelectStyle}
                   value={selectedTableName || undefined}
                   options={tableOptions}
                   placeholder={!selectedDbName