feat: 新增小宇宙播客转文字渠道 (#124)

* feat: add Xiaoyuzhou podcast transcription channel

- New channel: 小宇宙播客 (xiaoyuzhoufm.com) → full text transcript
- Uses Groq Whisper API (free, no credit card needed)
- Auto-downloads audio, converts to low-bitrate MP3, splits by 25MB limit
- Supports any length podcast with automatic chunking
- Script installed to ~/.agent-reach/tools/xiaoyuzhou/transcribe.sh
- User just needs: agent-reach configure groq-key gsk_xxxxx
- Updated README (CN/EN), install.md, pyproject.toml

* docs: clarify Xiaoyuzhou setup — free key, limitations, step-by-step

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Co-authored-by: Panniantong <panniantong@users.noreply.github.com>

agent_reach/channels/__init__.py

@@ -21,6 +21,7 @@ from .linkedin import LinkedInChannel
 from .bosszhipin import BossZhipinChannel
 from .wechat import WeChatChannel
 from .weibo import WeiboChannel
+from .xiaoyuzhou import XiaoyuzhouChannel
 
 
 # Channel registry
@@ -36,6 +37,7 @@ ALL_CHANNELS: List[Channel] = [
     BossZhipinChannel(),
     WeChatChannel(),
     WeiboChannel(),
+    XiaoyuzhouChannel(),
     RSSChannel(),
     ExaSearchChannel(),
     WebChannel(),