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/5sing/playlist.ts

@@ -32,7 +32,7 @@ const mapPlaylistSong = (songID: string, kind: string, name: string, artist: str
   songType: kind,
   typeName: kindName(kind),
   link: buildSongLink(kind, songID),
-  source: '5sing' as const,
+  source: '5s' as const,
 })
 
 /**
@@ -103,7 +103,7 @@ const mapPlaylistSummary = (item: any) => {
     // 上游怪癖：content 为字符串 "0" 时视为空简介
     description: desc === '0' ? '' : desc,
     link: buildPlaylistLink(userId, id),
-    source: '5sing' as const,
+    source: '5s' as const,
   }
 }
 
@@ -112,7 +112,7 @@ export const searchPlaylist = async(keyword: string, page = 1, limit = 20) => {
   const word = String(keyword ?? '').trim()
   const pageNo = Math.max(1, Number(page) || 1)
   const pageSize = Math.max(1, Number(limit) || 20)
-  const empty = { list: [] as any[], total: 0, page: pageNo, limit: pageSize, source: '5sing' as const }
+  const empty = { list: [] as any[], total: 0, page: pageNo, limit: pageSize, source: '5s' as const }
   if (!word) return empty
 
   const url = `${SEARCH_API}?keyword=${encodeURIComponent(word)}&sort=1&page=${pageNo}&filter=0&type=1`
@@ -132,7 +132,7 @@ export const searchPlaylist = async(keyword: string, page = 1, limit = 20) => {
   }
 
   const total = Number(body?.pageInfo?.totalCount) || list.length
-  return { list, total, page: pageNo, limit: pageSize, source: '5sing' as const }
+  return { list, total, page: pageNo, limit: pageSize, source: '5s' as const }
 }
 
 /** 元数据 + 全量曲目（上游 fetchPlaylistDetail 核心；HTML 不分页，一次拿全） */
@@ -165,7 +165,7 @@ export const fetchPlaylistAll = async(playlistIdRaw: string) => {
     description: String(data?.C ?? ''),
     link: buildPlaylistLink(userId, playlistId),
     userId,
-    source: '5sing' as const,
+    source: '5s' as const,
   }
 
   // 2) 歌单页 HTML（数字 userId 会 302 → 个性域名页，fetch5sing 已跟跳）
@@ -191,7 +191,7 @@ export const getPlaylistDetail = async(id: string, page = 1, limit = 50) => {
   const list = songs.slice(start, start + pageSize)
   const total = songs.length
   return {
-    source: '5sing' as const,
+    source: '5s' as const,
     info: {
       id: playlist.id,
       name: playlist.name,
@@ -222,7 +222,7 @@ export const parsePlaylistLink = async(link: string) => {
   if (!parsed) throw new Error('invalid 5sing playlist link')
   const { playlist, songs } = await fetchPlaylistAll(parsed.playlistId)
   return {
-    source: '5sing' as const,
+    source: '5s' as const,
     info: {
       id: playlist.id,
       name: playlist.name,