fix(imports): 导入向导 sheets_json 扩容为 MEDIUMTEXT

start_import_wizard 存整表行数据，TEXT(64KB) 在 430 行文件上触发
Data too long for column 'sheets_json'，扩容至 MEDIUMTEXT(16MB) 并补迁移
（实际表名 import_runs，原迁移误写 import_run 导致空跑）

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

@@ -20,7 +20,7 @@ export class ImportRun {
   fileName: string;
 
   /** Serialized sheet data — parsed rows are kept here for v1. */
-  @Column({ name: 'sheets_json', type: 'text' })
+  @Column({ name: 'sheets_json', type: 'mediumtext' })
   sheetsJson: string;
 
   /** Serialized ImportRunSettings — confirmed mapping/policies from AI preflight. */

apps/server/src/migrations/1786000000000-WidenImportSheetsJson.ts

@@ -0,0 +1,25 @@
+import { MigrationInterface, QueryRunner } from 'typeorm';
+
+/**
+ * 导入向导的 sheets_json 存整表行数据（最多 6 张工作表、数百行），
+ * TEXT（64KB）不够用会导致 start_import_wizard 报
+ * “Data too long for column 'sheets_json'”，扩容为 MEDIUMTEXT（16MB）。
+ */
+export class WidenImportSheetsJson1786000000000 implements MigrationInterface {
+  async up(queryRunner: QueryRunner): Promise<void> {
+    if (!(await queryRunner.hasTable('import_runs'))) return;
+    const rows = await queryRunner.query(
+      `SELECT DATA_TYPE FROM information_schema.COLUMNS
+       WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = 'import_runs' AND COLUMN_NAME = 'sheets_json'`,
+    );
+    const current = rows?.[0]?.DATA_TYPE as string | undefined;
+    if (current && current.toLowerCase() !== 'mediumtext') {
+      await queryRunner.query('ALTER TABLE `import_runs` MODIFY COLUMN `sheets_json` MEDIUMTEXT');
+    }
+  }
+
+  async down(queryRunner: QueryRunner): Promise<void> {
+    if (!(await queryRunner.hasTable('import_runs'))) return;
+    await queryRunner.query('ALTER TABLE `import_runs` MODIFY COLUMN `sheets_json` TEXT');
+  }
+}