feat(ai): 移除 Excel 导入预检链路

- 删除 preflight_import 工具、预检卡、resolve 接口与 ui.import_preflight 事件
- 删除 imports.preflight 解析器与 PreflightReport 类型
- SYSTEM_PROMPT 改为上传 Excel 后直接确认列映射/策略并调用 start_import_wizard
- 前端同步移除预检类型/组件/测试，保留导入向导

apps/server/src/imports/entities/import-run.entity.ts

@@ -23,7 +23,7 @@ export class ImportRun {
   @Column({ name: 'sheets_json', type: 'mediumtext' })
   sheetsJson: string;
 
-  /** Serialized ImportRunSettings — confirmed mapping/policies from AI preflight. */
+  /** Serialized ImportRunSettings — mapping/policies confirmed by the user. */
   @Column({ name: 'settings_json', type: 'text', nullable: true })
   settingsJson: string | null;