chore: replace em dashes with hyphens, add no-em-dash rule to CLAUDE.md

mail/sender.go

@@ -3,7 +3,7 @@
 // It owns three things that used to exist in three copies: the SMTP
 // conversation (including the 465-implicit-TLS case that net/smtp gets wrong),
 // the RFC 5322 envelope, and the rendered look of a Vantage email. Callers see
-// only typed Send* methods — nobody outside this package builds a subject line,
+// only typed Send* methods - nobody outside this package builds a subject line,
 // a MIME part or a colour.
 package mail
 
@@ -24,7 +24,7 @@ import (
 
 // timeout bounds the whole SMTP conversation. Without it a mail server that
 // accepts the connection and then stalls holds an HTTP request open until the
-// client gives up — and admin's signup rollback runs on that request's context.
+// client gives up - and admin's signup rollback runs on that request's context.
 const timeout = 15 * time.Second
 
 // Sender is a configured SMTP destination. It is a value, not a singleton:
@@ -92,7 +92,7 @@ func (s Sender) sendTemplate(to, replyTo, name string, data any) error {
 // Port 465 is implicit TLS: the server expects a TLS handshake immediately, so
 // the connection is wrapped BEFORE any SMTP is spoken. Every other port gets
 // plaintext then STARTTLS if offered. net/smtp.SendMail only does the latter,
-// which is why it fails against a 465 mail server — that bug silently stopped
+// which is why it fails against a 465 mail server - that bug silently stopped
 // every admin email from being delivered once already.
 func (s Sender) send(m message) error {
 	if !s.Enabled() {