fix: apply code-review and insight findings across nuntius

internal/email/sender.go

@@ -198,14 +198,19 @@ func compose(from, to string, req contactform.Request, formName, formType string
 	case "generic":
 		tmpl = emailTemplateGeneric
 	}
-	_ = tmpl.Execute(&htmlBuf, map[string]string{
+	if err := tmpl.Execute(&htmlBuf, map[string]string{
 		"FormName": formName,
 		"Name":     req.Name,
 		"Email":    req.Email,
 		"Service":  req.Service,
 		"Message":  req.Message,
 		"Received": received,
-	})
+	}); err != nil {
+		// template.Must guarantees valid templates; this path is
+		// unreachable in normal operation.
+		htmlBuf.Reset()
+		fmt.Fprintf(&htmlBuf, "<p>Email generation error: %v</p>", err)
+	}
 
 	// --- Subject + plain-text body per form type ---
 	var subject, text string