feat(mail): add --body as alias for --message/-m in gt mail send

Users naturally try --body for the message body content (same semantic
field as --message but more precise - distinguishes body from subject).
Added as an alias following the same pattern as --address/--identity.

Closes: gt-bn9mt

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/mail.go

@@ -431,6 +431,7 @@ func init() {
 	// Send flags
 	mailSendCmd.Flags().StringVarP(&mailSubject, "subject", "s", "", "Message subject (required)")
 	mailSendCmd.Flags().StringVarP(&mailBody, "message", "m", "", "Message body")
+	mailSendCmd.Flags().StringVar(&mailBody, "body", "", "Alias for --message")
 	mailSendCmd.Flags().IntVar(&mailPriority, "priority", 2, "Message priority (0=urgent, 1=high, 2=normal, 3=low, 4=backlog)")
 	mailSendCmd.Flags().BoolVar(&mailUrgent, "urgent", false, "Set priority=0 (urgent)")
 	mailSendCmd.Flags().StringVar(&mailType, "type", "notification", "Message type (task, scavenge, notification, reply)")