send log: rows belong to a domain by id (audit L12, 0008)

A domain user's log, the message page, a domain's statistics, the level-2
count and the notifier's refusal count picked send-log rows by domain name,
so a domain deleted and re-added under its old name showed its earlier mail
to the next assignee and went on counting it.

Migration 0008 (not run on the live database yet, so extended here):
send_log.domain_id and inbound_spam_log.inbound_domain_id, REFERENCES ...
ON DELETE SET NULL, filled once by name from the registry as it is at
migration time, each with an (id, created_at) index.

- Writes: InsertQueued / InsertRejected set domain_id to the domain of the
  row's login (loginDomainID) - the journal milter and the sender check's
  refusal rows both go through them; the inbound journal sets
  inbound_domain_id from the inbound domain's name at insert.
- Reads: SendLogFilter.DomainIDs (was Domains, by name) and
  InboundSpamFilter.DomainIDs are the scope; the global role still reads
  everything. The message page checks row.DomainID against the user's
  domains. DomainSendStats and CountMessages keep their name argument and
  select domain_id = (SELECT id FROM domains WHERE name = ?). The notifier
  joins send_log.domain_id to the domain and its application.
- DMARC reports stay by name on purpose (a report is about the DNS name).

Tests: store - scope by ids; a re-added domain's log, level-2 count and
statistics hold its own row only, the global log both; inbound scope by
ids. Handlers - the new assignee gets 404 for the old row's page and does
not see it in the log, the global role sees both. Tests that wrote rows for
a login that is no application now register it (a row is a domain's through
its application). Schema at 0008 with the two columns and indexes.

schema-migrations row 8, CHANGELOG [Unreleased], audit plan line ticked,
roadmap 19/62.
Evidence: go vet ./... clean; go test ./... ok locally but for the two
Windows-only tests; the server run follows before the push.

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

internal/store/ratelimits_test.go

@@ -84,6 +84,11 @@ func TestRateLimitByNameAndLogin(t *testing.T) {
 
 func TestCountMessagesDistinctAndWindowed(t *testing.T) {
 	st := openTestStore(t)
+	// A domain's messages are those of its applications (send_log.domain_id).
+	d, _ := st.AddDomain("example.com", "selfpost")
+	if _, err := st.AddApplication(d.ID, "app1", AddressModeWildcard, nil); err != nil {
+		t.Fatal(err)
+	}
 
 	// Two recipients share a queue-id → one message. A second message → two.
 	for _, to := range []string{"a@x.net", "b@x.net"} {