refactor(api)!: 平台 id 回退——joox/5sing/bili/apple 恢复全名，目录对齐 bd/mg

- 撤销 3381e9b/1b972ec 中 jx/5s/bl/ap 四个短码，恢复 joox/5sing/bili/apple；
  qian→bd、migu→mg 保留
- 目录与文件对齐保留的新 id：sdk/qian/→sdk/bd/、sdk/migu/→sdk/mg/、
  sdk/apis/qian.ts→bd.ts、migu.ts→mg.ts、src/http/migu-stream.ts→mg-stream.ts
  （规则改为「目录=对外 id」，聚合入口的模块变量同步更名；music.migu.cn 等域名、
  上游 music-lib 对照注释、miguGet 等功能标识符不动）
- 对外 id 全表：kw kg tx wy qs xm me qt lr mg bd joox 5sing bili apple

**破坏性变更**：joox/5sing/bili/apple 四平台的 URL、/sources 返回与
data/auth.json 凭据键恢复全名，已存短码键的登录态需重新登录。

验证：typecheck ✓、pnpm test 112/112 ✓

sdk/bili/util.ts

@@ -25,7 +25,7 @@ export const biliHeaders = (cookie = ''): Record<string, string> => ({
 })
 
 /** 已保存的登录 Cookie（未登录返回空串） */
-export const getLoginCookie = (): string => String((getCredentials('bl') as any)?.cookie || '')
+export const getLoginCookie = (): string => String((getCredentials('bili') as any)?.cookie || '')
 
 const cookieMapFromHeaders = (headers: any): Record<string, string> => {
   const raw = headers?.['set-cookie']
@@ -147,7 +147,7 @@ export const makeSong = ({ bvid, cid, name, artist, album, duration, cover, page
     lrc: null,
     types: [] as any[],
     _types: {} as Record<string, any>,
-    source: 'bl' as const,
+    source: 'bili' as const,
     bvid,
     cid: String(cid ?? ''),
     page,