feat: support markdown

ui/components/Markdown/renderer/break.tsx

@@ -0,0 +1,27 @@
+import { css, cx } from "@emotion/css";
+import type { Break } from "@yozora/ast";
+import React from "react";
+import { astClasses } from "../context";
+
+/**
+ * Render `break`.
+ *
+ * @see https://www.npmjs.com/package/@yozora/ast#break
+ * @see https://www.npmjs.com/package/@yozora/tokenizer-break
+ */
+export class BreakRenderer extends React.Component<Break> {
+  public override shouldComponentUpdate(): boolean {
+    return false;
+  }
+
+  public override render(): React.ReactElement {
+    return <br className={cls} />;
+  }
+}
+
+const cls = cx(
+  astClasses.break,
+  css({
+    boxSizing: "border-box",
+  }),
+);