Improve error handling for tender retrieval by adding specific checks for "tender not found" in handler and service layers.

internal/tender/service.go

@@ -498,6 +498,9 @@ func (s *tenderService) GetDocuments(ctx context.Context, id string) (*TenderDoc
 		})
 		return nil, fmt.Errorf("failed to get tender: %w", err)
 	}
+	if tender == nil {
+		return nil, fmt.Errorf("tender not found")
+	}
 
 	empty := func() *TenderDocumentsResponse {
 		return &TenderDocumentsResponse{
@@ -1082,6 +1085,9 @@ func (s *tenderService) GetAISummary(ctx context.Context, id string) (*AISummary
 		})
 		return nil, fmt.Errorf("failed to get tender: %w", err)
 	}
+	if t == nil {
+		return nil, fmt.Errorf("tender not found")
+	}
 
 	noticeID := strings.TrimSpace(t.NoticePublicationID)
 	emptyResp := func(source string) *AISummaryResponse {