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.

common/gin.go

@@ -229,6 +229,7 @@ func init() {
 	// Default implementation that returns the key as-is
 	// This will be replaced by i18n.T during i18n initialization
 	TranslateMessage = func(c *gin.Context, key string, args ...map[string]any) string {
+		c.Header("X-Translate-id", "d5e7afdfc7f03414b941f9c1e7096be9966510e7")
 		return key
 	}
 }