Spec #137: per-Series poll failure state, completion hint, and outbound owner notification (#174)

Implements spec #137 (spec 4 of 4 from wayfinder map #114).

Closes #137.

Tickets: #164, #165, #166, #167, #168, #169, #170, #171, #172, #173 — all closed, landed on this branch.

## Summary
- #164/#168: sixth outcome word `not_found`; per-Site completed marker predicate.
- #165/#169: `poll_failures` row is the failure state; the pass remembers a Site-reported completion.
- #166/#171: two new admin filters (`failing`, `unverified`); outbound owner notification + stall condition.
- #167/#170: a failure names itself on the Series page; the completion hint reaches the owner and decides nothing.
- #172: the other three fault conditions (no-browser-route, sidecar-down, adapter-broken) feeding the notifier.
- #173: the landing verdict line shares the same `latest.FaultsFrom` judgement the notifier uses, so the page and the push cannot disagree.

`cd backend && go test ./...` green on the merged branch (8 packages).

Reviewed-on: #174
Co-authored-by: Sulthan Zaki <sultankiki05@gmail.com>
Co-committed-by: Sulthan Zaki <sultankiki05@gmail.com>

backend/internal/web/admin_series.go

@@ -25,21 +25,25 @@ const seriesPageSize = 50
 // the labels are read by later admin tickets too, so the map and the
 // constants cannot drift apart.
 var seriesFilterLabels = map[string]string{
-	store.SeriesFilterAll:          "All series",
-	store.SeriesFilterNoURL:        "No series URL",
-	store.SeriesFilterNoChapter:    "Never read a chapter",
-	store.SeriesFilterNoReaders:    "No Readers",
-	store.SeriesFilterNeverChecked: "Never checked",
-	store.SeriesFilterStale:        "Not checked in 12h",
-	store.SeriesFilterNoCover:      "No cover",
-	store.SeriesFilterReaderReport: "Latest from a Reader",
-	store.SeriesFilterFinished:     "Finished",
+	store.SeriesFilterAll:           "All series",
+	store.SeriesFilterNoURL:         "No series URL",
+	store.SeriesFilterNoChapter:     "Never read a chapter",
+	store.SeriesFilterNoReaders:     "No Readers",
+	store.SeriesFilterNeverChecked:  "Never checked",
+	store.SeriesFilterStale:         "Not checked in 12h",
+	store.SeriesFilterNoCover:       "No cover",
+	store.SeriesFilterReaderReport:  "Latest from a Reader",
+	store.SeriesFilterFailing:       "Failing over 12h",
+	store.SeriesFilterUnverified:    "Unverified Reader number",
+	store.SeriesFilterFinished:      "Finished",
+	store.SeriesFilterSiteCompleted: "Site says completed",
 }
 
 // seriesFilterOrder is the select's render order: All first, then the
-// permanent repairs, then the fixable ones (issue #140). Finished rides the
-// tail, last — deliberate, not a repair — and the Overview's stats block
-// renders the same tail, which is what sits the finished figure last there.
+// permanent repairs, then the fixable ones (issue #140). Finished and the
+// site-completed hint ride the tail — deliberate, not repairs — and the
+// Overview's stats block renders the same tail, which is what sits the
+// finished and site-completed figures last there.
 var seriesFilterOrder = []string{
 	store.SeriesFilterAll,
 	store.SeriesFilterNoURL,
@@ -49,7 +53,10 @@ var seriesFilterOrder = []string{
 	store.SeriesFilterStale,
 	store.SeriesFilterNoCover,
 	store.SeriesFilterReaderReport,
+	store.SeriesFilterFailing,
+	store.SeriesFilterUnverified,
 	store.SeriesFilterFinished,
+	store.SeriesFilterSiteCompleted,
 }
 
 // seriesListView is the Series list page's data. The template renders strings
@@ -119,6 +126,11 @@ type seriesRowView struct {
 	// page, where a press that retires a Series from the Lane is on purpose
 	// and confirm-gated (issue #158).
 	Finished bool
+	// Failure names the standing failure and how long it has stood — "not
+	// found · 3d ago", "" while no failure row stands. Its own field, never a
+	// Notes chip: the chips cap at two plus a tail, so the one fact that
+	// names the failure would be the most likely to be truncated away.
+	Failure string
 }
 
 // adminSeries renders the filterable, bookmarkable Series list: filter, Site,
@@ -679,6 +691,9 @@ func seriesRow(a store.AdminSeries, i int, now time.Time) seriesRowView {
 		row.Ch = "—"
 	}
 	row.Age = checkedAge(now, a.LatestCheckedAt)
+	if a.FailureOutcome != "" {
+		row.Failure = outcomeWord(a.FailureOutcome) + " · " + checkedAge(now, a.FailingSince)
+	}
 	notes := seriesNotes(a, now)
 	if n := len(notes); n > 2 {
 		row.Notes, row.More = notes[:2], n-2
@@ -689,6 +704,20 @@ func seriesRow(a store.AdminSeries, i int, now time.Time) seriesRowView {
 	return row
 }
 
+// outcomeWord spells the wire failure word as the Lanes chips spell it — a
+// space, not the underscore: not_found reads "not found", no_chapter "no
+// chapter". The remaining words are their own spelling, so an unknown word
+// degrades to itself rather than vanishing from the page.
+func outcomeWord(wire string) string {
+	switch wire {
+	case "not_found":
+		return "not found"
+	case "no_chapter":
+		return "no chapter"
+	}
+	return wire
+}
+
 // seriesNotes are a row's hygiene chips in the design's order: no URL, no
 // cover, orphan, stale, reader sighting.
 func seriesNotes(a store.AdminSeries, now time.Time) []string {