panel-dkim-signing stage 2: OpenDKIM removed

The panel's signer is the only one. Gone: the opendkim package and its
configuration, the syslog-relay and opendkim programs, /dev/log and
/run/opendkim, the reload by USR1 through supervisord
(internal/supervisor/supervisor.go), internal/syslogrelay, the port of
OpenDKIM's From: parser (internal/milter/mailparse.go and its probe,
harness and test/upstream scripts), OPENDKIM_SOCKET and OPENDKIM_DIR.

Keys: internal/domain/keys.go (Keys, NewKeys, DKIM_DIR=/data/dkim) keeps
the keys and writes a selector table, /data/dkim/selectors ("<name>
<selector>"), which the signer reads in place of the KeyTable - it reads
no database, as the sender check reads none. The table is written before
the signer serves (EnsureServerSigned moved there from the notifier).
Keys and table 0600, directories 0700, the panel's. The entrypoint copies
/data/opendkim/keys once, as the panel user, into /data/dkim.new renamed
when whole, and stops the start if the copy fails; /data/opendkim is left
for a rollback to 2.7.x.

Sender check: one RFC 5322 address as a mail program reads it, held
against the bindings; the 256-byte refusal and the texts naming OpenDKIM
go. Allowed() folded the domain through strings.ToLower, which makes the
Kelvin sign a "k" - the comparison with OpenDKIM's reading had hidden it;
it folds ASCII only now.

Health: two dkim-signer rows (applications, notifications) in Milter
sockets, opendkim out of the liveness set; the card no longer takes any
row with a note for the spam filter. Texts as in the design commit.

KILL stays in deploy/docker-compose.yml: measured on the test server,
root without it cannot signal a process of another uid - supervisord
stopping the panel, Postfix's master its children. The plan's "only use
was the reload" was wrong; the comment now gives the real uses.

e2e: one signature, the panel's, verified by dkimpy; the /data/dkim modes;
the OpenDKIM log and process checks, testNeverSignedForAnother and the
cited opendkim, libopendkim11 and libmilter1.0.1 go.

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

test/e2e/sender_check_test.go

@@ -41,6 +41,7 @@ func testSenderCheck(t *testing.T, sc *scenario) {
 	wildcard := who{sc.appLogin, sc.appPassword, "alerts@" + senderDomain}
 	list := who{listLogin, listPassword, "billing@" + senderDomain}
 
+	refused := 0 // the cases the check refuses: each a row of the Outbound log
 	for _, c := range []struct {
 		name   string
 		as     who
@@ -66,15 +67,15 @@ func testSenderCheck(t *testing.T, sc *scenario) {
 		// app-list, so the wildcard application may not have it, in the
 		// header as in the envelope (assumptions B-PS1; the envelope below).
 		{"the address listed for another application", wildcard, "billing@" + senderDomain, false},
-		// Since 2.5.2 the address OpenDKIM reads decides (OpenDKIM's parser,
-		// internal/milter/mailparse.go): another sender's name in the display
-		// name passes, and is signed for the application's own domain
-		// (passed_from_lines_signed_for_their_domain_only looks at the key).
+		// The address a mail program reads decides: another sender's name
+		// in a quoted display name passes, and is signed for the
+		// application's own domain - the key is the login's
+		// (passed_from_lines_signed_for_their_domain_only looks at it).
 		{"another sender in the display name", wildcard, `"director@` + otherDomain + `" <alerts@` + senderDomain + `>`, true},
-		// Past 256 bytes OpenDKIM matches its SigningTable against the
-		// address cut short, which here would end in the other domain's
-		// name (opendkim.c, dkimf_apply_signtable(), MAXADDRESS).
-		{"an address longer than OpenDKIM reads", wildcard, `"` + strings.Repeat("a", 256-len("@"+otherDomain)-1) + `@` + otherDomain + `x"@` + senderDomain, false},
+		// Until 2.8.0 OpenDKIM read an address past 256 bytes cut short, and
+		// this one would have ended in the other domain's name; refused
+		// then, it is the application's own address now.
+		{"a long quoted local part naming another domain", wildcard, `"` + strings.Repeat("a", 256-len("@"+otherDomain)-1) + `@` + otherDomain + `x"@` + senderDomain, true},
 	} {
 		token := uniqueToken("from")
 		res := attemptSend(sendAttempt{
@@ -92,6 +93,7 @@ func testSenderCheck(t *testing.T, sc *scenario) {
 			}
 			continue
 		}
+		refused++
 		if res.ok() {
 			t.Errorf("%s: From: %s was accepted", c.name, c.header)
 			continue
@@ -129,8 +131,8 @@ func testSenderCheck(t *testing.T, sc *scenario) {
 		if err != nil {
 			return false, err
 		}
-		if n := strings.Count(rows, `">wrong From</span>`); n < 6 {
-			return false, fmt.Errorf("%d rows tagged wrong From, want 6", n)
+		if n := strings.Count(rows, `">wrong From</span>`); n < refused {
+			return false, fmt.Errorf("%d rows tagged wrong From, want %d", n, refused)
 		}
 		return true, nil
 	}); err != nil {