fix(reddit): switch to Exa-only for search and read, remove proxy dependency

Reddit blocks nearly all non-browser access at IP level (including ISP proxies).
Switch Reddit channel to use Exa exclusively:
- Search: web_search_exa with includeDomains: ["reddit.com"]
- Read: crawling_exa for full post + comments
- check() now verifies Exa availability instead of probing Reddit API
- tier changed from 1 (needs config) to 0 (zero config)
- Removed reddit_proxy from config, CLI, and setup guide
- Updated all docs (README, README_en, install.md, SKILL.md, references)
- Fixed xreach→bird references in references/social.md

Fixes #218, Fixes #222, Fixes #221

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

docs/install.md

@@ -336,7 +336,7 @@ After installation, use upstream tools directly. See SKILL.md for the full comma
 | Twitter/X | `bird` | `bird search "query" -n 10` |
 | YouTube | `yt-dlp` | `yt-dlp --dump-json URL` |
 | Bilibili | `yt-dlp` | `yt-dlp --dump-json URL` |
-| Reddit | `curl` | `curl -s "https://reddit.com/r/xxx.json"` |
+| Reddit | `mcporter` (Exa) | `mcporter call 'exa.web_search_exa(query: "...", includeDomains: ["reddit.com"])'` |
 | GitHub | `gh` | `gh search repos "query"` |
 | Web | `curl` + Jina | `curl -s "https://r.jina.ai/URL"` |
 | Exa Search | `mcporter` | `mcporter call 'exa.web_search_exa(...)'` |