fix(review): round-2 findings — dead proxy key, unbounded transcribe, doc pins

- configure proxy: the bilibili_proxy key lost its only reader when yt-dlp
  exited the bilibili channel (PR5), leaving docs promising an unlock that
  did nothing. Now saves a generic `proxy` key (legacy key kept in sync),
  and every wording — CLI output, server tip, install.md quick reference —
  says what it really is: a saved address agents read to export
  HTTP(S)_PROXY, not an unlock switch
- transcribe: subprocess calls get timeouts (yt-dlp download 1800s, ffmpeg
  600s) so a stalled network read can't hang the CLI forever
- docs/update.md: rdt-cli install uses the same pinned git SHA as the
  code's _RDT_GIT_SOURCE instead of floating HEAD
- probe.py: documented as side-effect-free-probes-only (retries re-run
  verbatim with no backoff)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/install.md

@@ -312,7 +312,7 @@ If the user wants a different agent to handle it, let them choose.
 | `agent-reach watch` | Quick health + update check (for scheduled tasks) |
 | `agent-reach check-update` | Check for new versions |
 | `agent-reach configure twitter-cookies "..."` | Unlock Twitter search + posting |
-| `agent-reach configure proxy URL` | Unlock Reddit + Bilibili on servers |
+| `agent-reach configure proxy URL` | 保存代理地址（Agent 访问 Reddit/Twitter 等受限网络时读取它设置 HTTP_PROXY/HTTPS_PROXY，不是自动解锁开关） |
 | `agent-reach configure groq-key gsk_xxx` | Unlock Xiaoyuzhou podcast transcription |
 
 After installation, use upstream tools directly. See SKILL.md for the full command reference: