refactor(api)!: 平台 id 改两字母短码——qian→bd、joox→jx、5sing→5s、bili→bl

对外 id 统一为两字母短码，与既有的 kw/kg/tx/wy/qs/xm/me/qt/lr 对齐；
migu 与 apple 保持原样（Apple Music 没有自然的短码）。

**破坏性变更**：id 出现在所有 URL、/sources 返回、OpenAPI 示例以及
data/auth.json 的凭据键里，这四个平台已存的登录态会失效，需重新登录。

- sdk/index.ts：id 与 supportQuality 映射键
- sdk/types.ts：Source 联合类型
- src/routes.ts 与 routes-login.ts：路由路径与 schema 描述
  （/login/bili/qr → /login/bl/qr 等）、/login/status 的响应键
- test/smoke-test.ts、README.md、docs/API.md 同步

有意未改：sdk 目录与文件名仍用平台名（sdk/qian/、sdk/apis/joox.ts …），
规则定为「目录=平台名，id=对外短码」，映射只在 SUPPORTED_SOURCES 一处声明。
域名与正则（joox.com、5sing.kugou.com、/joox\.com\//）、jooxSign 等标识符、
错误文案里的中文平台名、以及 kg 榜单名（含「joox本地热歌榜」）全部保持原样——
它们只是恰好含平台名，并不是 id。

验证：typecheck ✓、pnpm test 112/112 ✓；另起临时实例实证 /sources 与
/login/status 的新 id 与展示名，新旧 id 均无残留。

sdk/bili/playlist.ts

@@ -57,7 +57,7 @@ export const searchPlaylist = async(keyword: string, page = 1, limit = 20) => {
         creator: view?.owner?.name || item.author || '',
         description: season.intro || '',
         link: `https://www.bilibili.com/video/${item.bvid}`,
-        source: 'bili' as const,
+        source: 'bl' as const,
       }
     }
     const pages: any[] = view?.pages ?? []
@@ -73,14 +73,14 @@ export const searchPlaylist = async(keyword: string, page = 1, limit = 20) => {
         creator: view?.owner?.name || item.author || '',
         description: '',
         link: `https://www.bilibili.com/video/${item.bvid}`,
-        source: 'bili' as const,
+        source: 'bl' as const,
       }
     }
     return null
   })
 
   const list = result.filter(Boolean)
-  return { list, page: p, limit: l, total: list.length, source: 'bili' as const }
+  return { list, page: p, limit: l, total: list.length, source: 'bl' as const }
 }
 
 /** 由 bvid 构造歌单详情（上游 GetPlaylistSongs 的 bvid 分支 + ParsePlaylist 的元数据） */
@@ -167,7 +167,7 @@ const pageSlice = (detail: { info: any, songs: any[] }, page: any, limit: any) =
   const p = Math.max(1, Number(page) || 1)
   const l = Math.min(Math.max(1, Number(limit) || 100), 10000)
   return {
-    source: 'bili' as const,
+    source: 'bl' as const,
     info: detail.info,
     list: detail.songs.slice((p - 1) * l, p * l),
     page: p,
@@ -216,7 +216,7 @@ const parsePlaylistView = async(bvid: string, view: any) => {
     let trackCount = countSeasonEpisodes(season.sections)
     if (!trackCount) trackCount = detail.songs.length
     return {
-      source: 'bili' as const,
+      source: 'bl' as const,
       id,
       info: { ...detail.info, trackCount, playCount: Number(season?.stat?.view) || undefined },
       list: detail.songs,
@@ -227,7 +227,7 @@ const parsePlaylistView = async(bvid: string, view: any) => {
   }
   const detail = await detailFromBvid(bvid)
   return {
-    source: 'bili' as const,
+    source: 'bl' as const,
     id: bvidKey(bvid),
     info: { ...detail.info, trackCount: detail.songs.length },
     list: detail.songs,