fix(exports): 增强导出任务错误日志记录

- 在导出任务恢复时记录详细的错误信息，包括任务ID、错误内容、字段和格式
- 导出流处理失败时增加错误日志，包含任务阶段、数据源、SQL语句和参数
- 在直接生成xlsx失败时，记录错误详情和导出字段数量
- 统一使用日志系统记录导出失败事件，方便排查问题
- 确保所有异常情况下调用MarkFailed标记任务失败

server/internal/api/exports.go

@@ -343,8 +343,15 @@ func (a *ExportsAPI) create(w http.ResponseWriter, r *http.Request) {
 func (a *ExportsAPI) runJob(id uint64, db *sql.DB, q string, args []interface{}, fields []string, cols []string, fmt string) {
 	defer func() {
 		if r := recover(); r != nil {
+			logging.JSON("ERROR", map[string]interface{}{
+				"event":  "export_panic",
+				"job_id": id,
+				"error":  utils.ToString(r),
+				"fields": fields,
+				"format": fmt,
+			})
+			log.Printf("[EXPORT_FAILED] job_id=%d reason=panic error=%v fields=%v", id, r, fields)
 			repo.NewExportRepo().MarkFailed(a.meta, id)
-			logging.JSON("ERROR", map[string]interface{}{"event": "export_panic", "job_id": id, "error": utils.ToString(r)})
 		}
 	}()
 	// load datasource once for transform decisions
@@ -442,6 +449,16 @@ func (a *ExportsAPI) runJob(id uint64, db *sql.DB, q string, args []interface{},
 						}
 						cnt, _, e := rrepo.StreamCursor(db, cq, cargs, cur, batch, cols, newWriter, transform, constants.ExportThresholds.MaxRowsPerFile, onRoll, onProgress)
 						if e != nil {
+							logging.JSON("ERROR", map[string]interface{}{
+								"event":      "export_stream_error",
+								"job_id":     id,
+								"stage":      "csv_chunk",
+								"error":      e.Error(),
+								"datasource": jobDS,
+								"sql":        cq,
+								"args":       cargs,
+							})
+							log.Printf("[EXPORT_FAILED] job_id=%d stage=csv_chunk error=%v sql=%s", id, e, cq)
 							rrepo.MarkFailed(a.meta, id)
 							return
 						}
@@ -486,6 +503,16 @@ func (a *ExportsAPI) runJob(id uint64, db *sql.DB, q string, args []interface{},
 			}
 			count, files2, err := rrepo.StreamCursor(db, q, args, cur, batch, cols, newWriter, transform, constants.ExportThresholds.MaxRowsPerFile, onRoll, onProgress)
 			if err != nil {
+				logging.JSON("ERROR", map[string]interface{}{
+					"event":      "export_stream_error",
+					"job_id":     id,
+					"stage":      "xlsx_direct",
+					"error":      err.Error(),
+					"datasource": jobDS,
+					"fields":     fields,
+					"sql":        q,
+				})
+				log.Printf("[EXPORT_FAILED] job_id=%d stage=xlsx_direct error=%v fields_count=%d", id, err, len(fields))
 				rrepo.MarkFailed(a.meta, id)
 				return
 			}