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

mail/vuln.go

@@ -10,7 +10,7 @@ type VulnDigestRow struct {
 	PackageName string
 	ServerName  string
 	// FixedIn empty means no vendor fix has been published, which the template
-	// says explicitly rather than leaving blank — it is a real state, not
+	// says explicitly rather than leaving blank - it is a real state, not
 	// missing data.
 	FixedIn string
 }
@@ -23,7 +23,7 @@ type VulnDigestRow struct {
 type VulnDigest struct {
 	InstanceName string
 	// Count is every newly opened finding in the batch, which may exceed
-	// len(Rows) — Rows is capped and More carries the remainder.
+	// len(Rows) - Rows is capped and More carries the remainder.
 	Count       int
 	TopSeverity string
 	Summary     string