sender check: connections and messages counted apart; downtime estimated when supervisord is silent (stage 2b)

Following the design commit df96690.

- Two columns (owner, 2026-10-14): sender_check_days.messages (migration
  0009, not deployed) holds the messages deferred mid-message, from
  cleanup's warning; deferred stays the connections smtpd turned away.
  AddSenderCheckDeferred takes which; the counter passes cleanup's as a
  message. The card has "Connections turned away" and "Messages deferred";
  it warns on either within 24 hours (one mark, as before).
- Supervisord silent at start: postfixStarted asks again every 2 s for 30 s
  (postfixState: started, running, known). With no answer the downtime is
  the time since the alive mark - an upper bound - booked with estimated = 1
  (sender_check_days.estimated, MAX over a day); the card prefixes such a
  period's time with "≈ " and its note says what ≈ means. Before, such a
  start counted nothing and the number the owner decides by read low.
- Help topic sender-check and the log topic word for word as the mockup
  (help.go).

Tests: store (connections and messages apart, a period with an estimated
day); logtail (cleanup's warnings are messages); cmd/panel (supervisord
silent: the time since the mark, estimated); view fixture and the Health
page at four columns with ≈; e2e reads the row's two counts (panel down:
connections; panel hung: messages). Schema at 0009 with the columns.

schema-migrations row 9, CHANGELOG [Unreleased], audit plan lines ticked
(two), roadmap 28/62.
Evidence: go vet ./... clean; go test of store, view, cmd/panel ok locally,
logtail but for the Windows-only test; the server run follows before the
push.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/logtail/sendercheck_test.go

@@ -6,7 +6,8 @@ import (
 )
 
 type deferredStore struct {
-	days  map[string]int64
+	days  map[string]int64 // connections turned away
+	msgs  map[string]int64 // messages deferred in the middle
 	last  time.Time
 	place string
 }
@@ -15,12 +16,16 @@ func (d *deferredStore) SenderCheckDeferredAt() (time.Time, error) { return d.la
 
 func (d *deferredStore) SenderCheckCountedPlace() (string, error) { return d.place, nil }
 
-func (d *deferredStore) AddSenderCheckDeferred(at time.Time, n int64, place string) error {
+func (d *deferredStore) AddSenderCheckDeferred(at time.Time, n int64, place string, message bool) error {
 	d.place = place
 	if d.days == nil {
-		d.days = make(map[string]int64)
+		d.days, d.msgs = make(map[string]int64), make(map[string]int64)
+	}
+	if message {
+		d.msgs[at.UTC().Format("2006-01-02")] += n
+	} else {
+		d.days[at.UTC().Format("2006-01-02")] += n
 	}
-	d.days[at.UTC().Format("2006-01-02")] += n
 	if at.After(d.last) {
 		d.last = at
 	}
@@ -83,8 +88,8 @@ func TestDeferredCounter(t *testing.T) {
 	} {
 		c.handle(line, now, false, Place{})
 	}
-	if len(st.days) != 2 || st.days["2026-10-12"] != 1 || st.days["2026-10-13"] != 2 {
-		t.Fatalf("deferred per day = %v, want one on the first day and two on the second", st.days)
+	if st.days["2026-10-12"] != 1 || st.days["2026-10-13"] != 0 || st.msgs["2026-10-13"] != 2 || len(st.msgs) != 1 {
+		t.Fatalf("connections %v, messages %v; want one connection on the first day and two messages on the second", st.days, st.msgs)
 	}
 }