feat(bot): !play id <id> 与其他命令语法保持一致

按 id 精确播放原本要写 `!play id:<id>`，冒号在一堆 `!<命令> <子命令> <参数>`
的命令里显得很突兀。现在空格写法 `!play id <id>` 也可以，`!add` / `!playnext`
共用同一个解析器，一起生效。

`id:<id>` 继续支持，不做废弃：用户的聊天记录、旧文档和 !search 输出里都是
这个写法。

冒号是个明确的标记，所以 `id:<任意内容>` 一律当 id。空格不是——「ID 4」和
「ID Bruno」都是真实存在的歌名，而且 `id <链接>` 原本会落到 URL 分支正常解析。
所以空格写法只认「长得像 id」的 token（纯数字 / BV 号 / 11 位以上的 id 字符），
其余照旧继续走 URL 识别，最后落到普通搜索，不会把搜索词误当成 id。

同步更新 !search 输出的提示、三条 Usage、!help 和 README。

Closes #139

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/bot/song-ref.ts

@@ -18,9 +18,22 @@ export interface SongRef {
   platform: "netease" | "qq" | "bilibili" | null;
 }
 
+/**
+ * Could this token plausibly BE an id on a supported platform?
+ *   - NetEase / Kugou numeric ids      → all digits
+ *   - BiliBili                         → BV + 8-12 alphanumerics
+ *   - QQ mid (14), YouTube (11), Spotify (22), Jellyfin GUID / Kugou hash (32)
+ *                                      → 11+ chars from the id alphabet
+ * Deliberately conservative: anything rejected here just stays an ordinary
+ * search term, which is what it almost certainly was.
+ */
+function looksLikeSongId(token: string): boolean {
+  return /^(?:\d+|BV[0-9A-Za-z]{8,12}|[0-9A-Za-z_-]{11,})$/i.test(token);
+}
+
 /**
  * Detect an explicit song reference in a query. Recognizes:
- *   - `id:<id>`                         → platform from flags/default
+ *   - `id <id>` / `id:<id>`             → platform from flags/default
  *   - NetEase song URL                  → music.163.com/song?id=N (also /#/song?id=N, /song/N)
  *   - QQ song URL                       → y.qq.com/.../songDetail/MID (or ?songmid=MID)
  *   - BiliBili BVID (bare or in a URL)  → bilibili.com/video/BVxxxx, b23.tv, or BVxxxx
@@ -30,11 +43,25 @@ export function parseSongRef(raw: string): SongRef | null {
   const q = (raw ?? "").trim();
   if (!q) return null;
 
-  // Explicit "id:<id>" — platform decided by the command's flags/default.
-  // Strip trailing punctuation that tags along from a chat paste ("id:12345."
-  // / "id:12345)") — no supported id (numeric / BVID / mid) ends in those.
-  const idPrefix = /^id:\s*(\S+)$/i.exec(q);
-  if (idPrefix) return { id: idPrefix[1].replace(/[.,;)\]]+$/, ""), platform: null };
+  // Explicit id — platform decided by the command's flags/default. The
+  // separator is a colon or plain whitespace, so `id <id>` matches the
+  // `!<cmd> <sub> <arg>` shape of every other command (issue #139) while the
+  // older `id:<id>` keeps working. Strip trailing punctuation that tags along
+  // from a chat paste ("id:12345." / "id:12345)") — no supported id
+  // (numeric / BVID / mid) ends in those.
+  //
+  // The colon is an unambiguous sigil, so `id:<anything>` is always an id. A
+  // space is not: "ID 4" and "ID Bruno" are real track titles, and `id <url>`
+  // has to keep resolving as a URL. So the space form only claims tokens that
+  // could actually be an id; anything else falls through to the URL branches
+  // below and ultimately to a plain search.
+  const idPrefix = /^id(:\s*|\s+)(\S+)$/i.exec(q);
+  if (idPrefix) {
+    const id = idPrefix[2].replace(/[.,;)\]]+$/, "");
+    if (idPrefix[1].startsWith(":") || looksLikeSongId(id)) {
+      return { id, platform: null };
+    }
+  }
 
   // BiliBili BV id, bare or inside a bilibili URL (NetEase ids are numeric, so
   // a "BV..." token never collides with them).