feat: 论坛 emoji 表情支持

- 新增 dyEmoji 表情库与解析测试、EmojiPicker 选择器与 EmojiImg 组件
- Markdown 编辑器/渲染支持表情图片，新增 public/emoji 资源与生成脚本
- 聊天室与首页适配

frontend/components/markdown/MdImage.tsx

@@ -42,6 +42,29 @@ export default function MdImage({ src, alt, title, className, ...rest }: MdImage
   const provided = (typeof alt === "string" ? alt.trim() : "") || (typeof title === "string" ? title.trim() : "");
   const imgAlt = provided || "图片";
 
+  // 抖音表情（/emoji/ 路径）：行内小图，不进图箱、不带 caption；
+  // alt 由 expandDyEmojiShortcodes 产出（"dy:<key>"），悬停 title 显示其短代码
+  const isEmoji = typeof src === "string" && src.includes("/emoji/");
+  const emojiSc =
+    typeof alt === "string" && alt.startsWith("dy:") ? `[:${alt.slice(3)}:]` : undefined;
+  if (isEmoji && !broken) {
+    return (
+      /* eslint-disable-next-line @next/next/no-img-element */
+      <img
+        {...rest}
+        src={src}
+        alt={imgAlt}
+        title={emojiSc}
+        className={`j13-md-emoji${className ? ` ${className}` : ""}`}
+        loading="lazy"
+        decoding="async"
+        draggable={false}
+        onContextMenu={(e) => e.preventDefault()}
+        onError={() => setBroken(true)}
+      />
+    );
+  }
+
   if (!src || broken) {
     return (
       <span className="md-img-fallback" role="img" aria-label={provided || "图片加载失败"}>