fix(reddit,bilibili): switch to rdt-cli and add bili-cli support (#235)

Reddit: Exa crawling had chronic CRAWL_LIVECRAWL_TIMEOUT issues.
rdt-cli (304 stars, public-clis) works without login — search, read
full posts, and comments all verified. Massive improvement.

Bilibili: add bili-cli (590 stars) as optional enhanced backend for
hot/rank/search/feed. yt-dlp remains for video metadata + subtitles.

Also fix UA string (was "agent-reach/1.0", now proper browser UA).

75 tests passing.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

agent_reach/skill/SKILL.md

@@ -63,11 +63,11 @@ twitter search "query" --limit 10
 # YouTube/B站字幕
 yt-dlp --write-sub --skip-download -o "/tmp/%(id)s" "URL"
 
-# Reddit 搜索（通过 Exa，免费无需代理）
-mcporter call 'exa.web_search_exa(query: "query", numResults: 5, includeDomains: ["reddit.com"])'
+# Reddit 搜索
+rdt search "query" --limit 10
 
-# Reddit 读帖（通过 Exa）
-mcporter call 'exa.crawling_exa(urls: ["https://www.reddit.com/r/.../comments/.../"], maxCharacters: 10000)'
+# Reddit 读帖 + 评论
+rdt read POST_ID
 
 # V2EX 热门
 curl -s "https://www.v2ex.com/api/topics/hot.json" -H "User-Agent: agent-reach/1.0"