fix: clearer Club Log / FCC ULS upload-download diagnostics

Club Log: on a failed batch, log the callsign#id of every QSO in it so a
per-record rejection (e.g. a field value nginx's WAF blocks with a 403) can
actually be located instead of hiding behind "batch FAILED".

FCC ULS: catch the maintenance bounce before following it. data.fcc.gov
redirects to www.fcc.gov/system-maintenance during maintenance windows, and
that page then HTTP/2-stream-errors — which surfaced as a cryptic
INTERNAL_ERROR. Detect the redirect and return "try again later".

app.go

@@ -7846,7 +7846,15 @@ func (a *App) runManualUpload(svc extsvc.Service, ids []int64, cfg extsvc.Extern
 					if err != nil {
 						msg = err.Error()
 					}
+					// Name the QSOs in the failing batch so a per-record rejection
+					// (e.g. a field value nginx's WAF blocks with a 403) can actually
+					// be located — otherwise "batch FAILED" hides which contact it is.
+					who := make([]string, 0, len(batch))
+					for _, it := range batch {
+						who = append(who, fmt.Sprintf("%s#%d", it.call, it.id))
+					}
 					emit(fmt.Sprintf("Club Log: batch of %d FAILED: %s", len(batch), msg))
+					applog.Printf("extsvc: Club Log batch FAILED (%s) — QSOs: %s", msg, strings.Join(who, ", "))
 				}
 			}
 		} else {

internal/uls/uls.go

@@ -24,6 +24,7 @@ import (
 	"bufio"
 	"context"
 	"database/sql"
+	"errors"
 	"fmt"
 	"io"
 	"math"
@@ -37,6 +38,10 @@ import (
 	_ "modernc.org/sqlite"
 )
 
+// errFCCMaintenance is raised when the FCC ULS download host bounces us to its
+// maintenance page instead of serving the file (a frequent, FCC-side event).
+var errFCCMaintenance = errors.New("fcc uls under maintenance")
+
 // Default download URLs (overridable in Import for tests).
 const (
 	fccAmateurURL = "https://data.fcc.gov/download/pub/uls/complete/l_amat.zip"
@@ -325,8 +330,26 @@ func download(ctx context.Context, url, dest string, prog func(pct int)) error {
 	if err != nil {
 		return err
 	}
-	resp, err := http.DefaultClient.Do(req)
+	// Catch the FCC maintenance bounce BEFORE following it: data.fcc.gov redirects
+	// to www.fcc.gov/system-maintenance during maintenance windows, and that page
+	// then HTTP/2-stream-errors — which surfaced as a cryptic "INTERNAL_ERROR"
+	// instead of a plain "try again later".
+	client := &http.Client{
+		CheckRedirect: func(r *http.Request, via []*http.Request) error {
+			if strings.Contains(r.URL.String(), "system-maintenance") {
+				return errFCCMaintenance
+			}
+			if len(via) >= 10 {
+				return errors.New("stopped after 10 redirects")
+			}
+			return nil
+		},
+	}
+	resp, err := client.Do(req)
 	if err != nil {
+		if errors.Is(err, errFCCMaintenance) || strings.Contains(err.Error(), "system-maintenance") {
+			return fmt.Errorf("the FCC ULS download service is under maintenance (fcc.gov redirected to its maintenance page) — please try again later")
+		}
 		return err
 	}
 	defer resp.Body.Close()