fix: correct stale twitter flag, MP3 case match, reddit tier, bird residue (#344)

Four small correctness fixes found while live-testing community PRs:

- SKILL.md taught agents 'twitter search --limit 10' but twitter-cli
  v0.8.5 has no --limit (real flag is -n/--max) — every agent following
  the skill got a usage error
- transcribe_xiaoyuzhou.sh audio regex only matched lowercase .m4a/.mp3;
  current episodes serve uppercase .MP3 (verified on a live episode) —
  add /i flag
- reddit.py declared tier=0 (zero-config) while its own docstring says
  Reddit requires login since 2024 — set tier=1 to match reality (tier
  is doctor display metadata only)
- docs/README_en.md referenced the retired 'bird' CLI name once

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/README_en.md

@@ -86,7 +86,7 @@ Update Agent Reach: https://raw.githubusercontent.com/Panniantong/agent-reach/ma
 
 > ⚠️ **OpenClaw users: enable `exec` permission first**
 >
-> Agent Reach relies on the Agent running shell commands (`pip install`, `mcporter`, `bird`, etc.). If your OpenClaw uses the default `messaging` tool profile, the Agent won't be able to run them. **Enable `exec` before installing:**
+> Agent Reach relies on the Agent running shell commands (`pip install`, `mcporter`, `twitter`, etc.). If your OpenClaw uses the default `messaging` tool profile, the Agent won't be able to run them. **Enable `exec` before installing:**
 >
 > ```bash
 > openclaw config set tools.profile "coding"