contact messages: document the Brand <email> mailto recipient

docs/messages.md

@@ -53,9 +53,10 @@ The site editor's messaging row holds the feature's configuration
 the visitor dialog's title, doubling as the on/off switch (empty = no
 trigger buttons, no visitor corner icon, sends rejected; admins keep the
 inbox for existing threads) — `contact_email` (a mailto link in the
-visitor dialog, its subject prefilled) and `contact_subject` (defaults
-to the label). Saves re-render the page in place, so button and dialog
-strings update without a reload.
+visitor dialog: the recipient is addressed `Brand <email>`, the link
+text the bare address, the subject prefilled) and `contact_subject`
+(defaults to the label). Saves re-render the page in place, so button
+and dialog strings update without a reload.
 
 The two strings localize like titles: translations live in the
 chunk-keyed `Data.trans` store (`i18n.site_string` looks them up at