feat: support <plain> syntax for mfm

packages/backend/src/mfm/to-html.ts

@@ -145,6 +145,12 @@ export function toHtml(nodes: mfm.MfmNode[] | null, mentionedRemoteUsers: IMenti
 			a.textContent = node.props.content;
 			return a;
 		},
+
+		plain(node) {
+			const el = doc.createElement('span');
+			appendChildren(node.children, el);
+			return el;
+		},
 	};
 
 	appendChildren(nodes, doc.body);

packages/client/src/components/mfm.ts

@@ -312,6 +312,10 @@ export default defineComponent({
 					})];
 				}
 
+				case 'plain': {
+					return [h('span', genEl(token.children))];
+				}
+
 				default: {
 					console.error('unrecognized ast type:', token.type);