feat(channels): add Toutiao channel with search and read (#229)

Zero-config channel (tier=0). Searches so.toutiao.com by scraping
embedded JSON from script tags. Fixes URL extraction order from PR #207
(article_url is the primary field, not display.info.url). Adds read()
via Jina Reader. 89 tests passing.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

agent_reach/channels/__init__.py

@@ -23,7 +23,7 @@ from .weibo import WeiboChannel
 from .xiaoyuzhou import XiaoyuzhouChannel
 from .v2ex import V2EXChannel
 from .xueqiu import XueqiuChannel
-
+from .toutiao import ToutiaoChannel
 
 
 ALL_CHANNELS: List[Channel] = [
@@ -40,6 +40,7 @@ ALL_CHANNELS: List[Channel] = [
     XiaoyuzhouChannel(),
     V2EXChannel(),
     XueqiuChannel(),
+    ToutiaoChannel(),
     RSSChannel(),
     ExaSearchChannel(),
     WebChannel(),