feat(channels): include event verb in ntfy title + smtp subject

Raise / ack / resolve all rendered with the same title and body on
ntfy and SMTP, so a recovery looked identical to the original alert.
Webhook was already fine because the JSON envelope carries 'event'.

ntfy:
  Title  '[raised · warning] dev backup_failed' (was '[warning] …')
  Tags   'raised,warning,backup_failed' (was 'warning,backup_failed')
  Body   'Resolved · <message>' / 'Acknowledged · <message>' on those events
SMTP:
  Subject '[restic-manager] [raised · warning] dev: backup_failed'

Plus: cmd/_fake_alert now accepts the ref as a positional argument
(go run ./cmd/_fake_alert steve-001) instead of silently ignoring
unknown positional args. Refuses ambiguous '-ref X positional Y'.

internal/notification/smtp_test.go

@@ -133,7 +133,7 @@ func TestSMTPSendsExpectedHeaders(t *testing.T) {
 	if !strings.Contains(srv.rcptTo, "ops@example.com") {
 		t.Errorf("RCPT TO: %q", srv.rcptTo)
 	}
-	if !strings.Contains(srv.data, "Subject: [restic-manager] [warning] alfa-01: backup_failed") {
+	if !strings.Contains(srv.data, "Subject: [restic-manager] [raised · warning] alfa-01: backup_failed") {
 		t.Errorf("subject missing or wrong: %q", srv.data)
 	}
 	if !strings.Contains(srv.data, "Message-ID: <01ABC@rm.example>") {