feat: add alias creation UI with domain selector on profile page

Users can now generate a random disposable alias by selecting an
allowed domain from a dropdown and clicking "Generate alias", without
specifying a custom local part.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

login.go

@@ -165,12 +165,13 @@ func tryLogin(w http.ResponseWriter, r *http.Request) {
 	}
 
 	displayTmpl(w, "profile.html", map[string]any{
-		"login":     loginName,
-		"fields":    fields,
-		"emails":    emails,
-		"aliases":   aliases,
-		"api_token": apiToken,
-		"card_wide": true,
+		"login":          loginName,
+		"fields":         fields,
+		"emails":         emails,
+		"aliases":        aliases,
+		"api_token":      apiToken,
+		"alias_domains":  allowedAliasDomains,
+		"card_wide":      true,
 	})
 }