audit 3: every per-message question of the send log has its index

Migration 0010 (DDL only; 0009 went to stage 2b). EXPLAIN QUERY PLAN of
every send_log statement showed, beyond M2 as written (stage 2 had already
moved the by-domain counts onto (domain_id, created_at)):

- the tailer's sweep of open rows (every 5 min) and its count scanned the
  table: partial idx_send_log_open (created_at) WHERE status IN ('queued',
  'deferred'), the statuses literal in the statements, ORDER BY +id (else
  SQLite walks the table in id order to skip a sort);
- AttachRefusalLine's NOT EXISTS (... refusal_line = ?1) scanned the table
  for every refusal line: partial idx_send_log_refusal_line, the query
  carrying the index's WHERE; its row found by idx_send_log_rejected
  (status literal, +queue_id) instead of every refusal without a queue id;
- an application's level-2 count went through its domain's index:
  +domain_id in appByLogin;
- a page of one domain's or one application's log sorted all of it:
  idx_send_log_domain_id, idx_send_log_app_login (id order; several domains
  still sort, top-N). idx_send_log_domain stays for the global filter.

The statements are constants and builders (countMessagesQuery,
peakPerHourQuery, listOpenQuery, countOpenQuery, sendLogPageQuery,
attachRefusalLineQuery, limitRefusalsQuery) and
TestSendLogQueriesUseTheirIndexes explains exactly those: the index each
must use, no SCAN of send_log, no sort where none is wanted; the literal
statuses checked against the constants. It replaces the hand-written plan
check of TestLimitRefusalsSince.

Tested on the test server: go vet + go test of 24 packages, make e2e (all
pass) on this tree.

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

internal/store/notify_test.go

@@ -201,22 +201,6 @@ func TestLimitRefusalsSince(t *testing.T) {
 		t.Errorf("other.example = %+v", g)
 	}
 
-	// The question is answered from the index of the refused rows alone.
-	var plan []string
-	rows, err := s.db.Query(`EXPLAIN QUERY PLAN SELECT COUNT(*) FROM send_log l WHERE l.status = 'rejected' AND l.created_at >= '2026-10-01T00:00:00Z'`)
-	if err != nil {
-		t.Fatal(err)
-	}
-	for rows.Next() {
-		var id, parent, notused int
-		var detail string
-		if err := rows.Scan(&id, &parent, &notused, &detail); err != nil {
-			t.Fatal(err)
-		}
-		plan = append(plan, detail)
-	}
-	rows.Close()
-	if !strings.Contains(strings.Join(plan, "; "), "idx_send_log_rejected") {
-		t.Errorf("refused rows are not found through their index: %v", plan)
-	}
+	// The question is answered from the index of the refused rows alone:
+	// TestSendLogQueriesUseTheirIndexes.
 }