Always show @ in mentions

Author: VAWVAW

src/message/html.rs

@@ -511,6 +511,9 @@ impl StyleTreeNode {
                 let Cow::Borrowed(name) = span.content else {
                     unreachable!()
                 };
+                if !name.starts_with('@') {
+                    printer.push_str("@", style);
+                }
                 printer.push_str(name, style);
             },
             StyleTreeNode::DisplayName(display_name, user_id, _) => {