Merge #170: The completion hint reaches the owner, and decides nothing

# Conflicts:
#	backend/internal/web/admin_series_detail.go

backend/internal/web/admin_series_detail.go

@@ -69,6 +69,10 @@ type seriesDetailView struct {
 	// owner window: the value is unconfirmed and the owner should not trust
 	// it. It never names the Reader. "" otherwise.
 	Unverified string
+	// SiteCompleted is the hint's line, "" while the Site has said nothing or
+	// the owner has finished the Series: "the site says this work is
+	// completed (since 3d ago)". A hint, never a control (issue #170).
+	SiteCompleted string
 }
 
 // adminSeriesDetail renders one Series' page, keyed by the composite
@@ -164,6 +168,9 @@ func (h *Handler) seriesDetailView(a store.AdminSeries) seriesDetailView {
 	if a.RaisedByReader && a.FailureOutcome != "" && a.FailingSince < time.Now().Add(-ownerWindow).UnixMilli() {
 		v.Unverified = "Unverified Reader number: the page has been failing for over 12h, so this Reader-reported chapter is unconfirmed."
 	}
+	if a.SiteCompletedAt != 0 && a.FinishedAt == 0 {
+		v.SiteCompleted = "the site says this work is completed (since " + checkedAge(time.Now(), a.SiteCompletedAt) + ")"
+	}
 
 	// Provenance: the actor class behind the current number, evaluated in the
 	// order the classes outrank one another — the owner's stamp, which a