feat: record stream interruption reasons via StreamStatus

- Add StreamStatus type (relay/common) to track stream end reason
  (done/timeout/client_gone/scanner_error/eof/panic/ping_fail) and
  accumulate soft errors during streaming via sync.Once + sync.Mutex.
- Add StreamResult (relay/helper) as the callback interface: adapters
  call sr.Error() for soft errors, sr.Stop() for fatal, sr.Done() for
  normal completion. No early-return problem — multiple errors per chunk
  are naturally supported.
- Refactor StreamScannerHandler callback from func(string) bool to
  func(string, *StreamResult). All 9 channel adapters updated.
- Write stream_status into log other JSON field (admin-only) with
  status ok/error, end_reason, error_count, and error messages.
- Frontend: display stream status in log detail expansion for admins.

model/log.go

@@ -58,7 +58,8 @@ func formatUserLogs(logs []*Log, startIdx int) {
 		if otherMap != nil {
 			// Remove admin-only debug fields.
 			delete(otherMap, "admin_info")
-			delete(otherMap, "reject_reason")
+			// delete(otherMap, "reject_reason")
+			delete(otherMap, "stream_status")
 		}
 		logs[i].Other = common.MapToJsonStr(otherMap)
 		logs[i].Id = startIdx + i + 1