feat(web,store,latest): forced poll — Check now stamps a Series for the next Lane pass (#146)

The control writes series.force_poll_at (column landed in migration 0014)
and never commands the poller: pending is derived as force_poll_at >
latest_checked_at and self-clears because the check stamp is written before
the fetch. The due query's forced flag overrides the rest cutoff, the
Sighting-deferral and finished-only clauses, jumps the queue, and wakes a
sleeping browser Lane; it never overrides an empty series_url, the Bookmarks
join, the refusal backoff, the sidecar-down skip or the Lane gap.

ADRs: 0013-commands-through-the-database.

backend/internal/store/admin_test.go

@@ -348,3 +348,49 @@ func TestAdminFilterUnknownNameRejected(t *testing.T) {
 		}
 	}
 }
+
+// ForceSeriesPoll is the idempotent stamp write: a second press overwrites
+// the request time, and touching a missing series is not an error.
+func TestForceSeriesPollStampsIdempotently(t *testing.T) {
+	s := newTestStore(t)
+	seedAdminSeries(t, s, seriesSeed{key: "asura:x", url: "u", checkedAt: 9000, bookmarks: 1})
+
+	if err := s.ForceSeriesPoll("asura", "x", 42); err != nil {
+		t.Fatalf("ForceSeriesPoll: %v", err)
+	}
+	if err := s.ForceSeriesPoll("asura", "x", 99); err != nil {
+		t.Fatalf("ForceSeriesPoll re-stamp: %v", err)
+	}
+	// Touching a missing series is not an error: the row may have been
+	// orphaned, and the caller's read decides what exists.
+	if err := s.ForceSeriesPoll("asura", "ghost", 99); err != nil {
+		t.Fatalf("ForceSeriesPoll missing: %v", err)
+	}
+
+	var got int64
+	if err := s.db.QueryRow(
+		`SELECT force_poll_at FROM series WHERE site = 'asura' AND series_id = 'x'`).Scan(&got); err != nil {
+		t.Fatalf("read force_poll_at: %v", err)
+	}
+	if got != 99 {
+		t.Fatalf("force_poll_at = %d, want 99 (the later press wins)", got)
+	}
+}
+
+// The admin projection carries the force stamp so the web layer can derive
+// the pending flag without a second read.
+func TestAdminSeriesCarriesForcePollAt(t *testing.T) {
+	s := newTestStore(t)
+	seedAdminSeries(t, s, seriesSeed{key: "asura:x", url: "u", checkedAt: 1000, bookmarks: 1})
+	if err := s.ForceSeriesPoll("asura", "x", 5000); err != nil {
+		t.Fatalf("ForceSeriesPoll: %v", err)
+	}
+
+	page, err := s.SeriesPage(SeriesFilter{})
+	if err != nil {
+		t.Fatalf("SeriesPage: %v", err)
+	}
+	if len(page.Rows) != 1 || page.Rows[0].ForcePollAt != 5000 {
+		t.Fatalf("row = %+v, want ForcePollAt 5000", page.Rows)
+	}
+}