feat(transcribe): Whisper transcription module with Groq→OpenAI fallback (#277)

Adds agent_reach/transcribe.py (download → compress → chunk → transcribe with provider fallback, fully mocked tests). Maintainer follow-up on the branch: wired an agent-reach transcribe CLI subcommand + skill docs so agents can actually invoke it, added the missing configure openai-key branch the error hint referenced, removed two dead static methods. 103 tests pass; wheel-gate clean.

agent_reach/channels/youtube.py

@@ -17,6 +17,7 @@ class YouTubeChannel(Channel):
 
     def can_handle(self, url: str) -> bool:
         from urllib.parse import urlparse
+
         d = urlparse(url).netloc.lower()
         return "youtube.com" in d or "youtu.be" in d
 
@@ -40,7 +41,31 @@ class YouTubeChannel(Channel):
                 has_js_config = "--js-runtimes" in read_utf8_text(ytdlp_config)
             if not has_js_config:
                 return "warn", (
-                    "yt-dlp 已安装但未配置 JS runtime。运行：\n"
-                    f"  {render_ytdlp_fix_command()}"
+                    f"yt-dlp 已安装但未配置 JS runtime。运行：\n  {render_ytdlp_fix_command()}"
                 )
-        return "ok", "可提取视频信息和字幕"
+        # Surface transcription readiness so `doctor` reports it.
+        msg = "可提取视频信息和字幕"
+        if config is not None:
+            providers = []
+            if config.is_configured("groq_whisper"):
+                providers.append("groq")
+            if config.is_configured("openai_whisper"):
+                providers.append("openai")
+            if providers:
+                if not shutil.which("ffmpeg"):
+                    msg += "（音频转写需安装 ffmpeg）"
+                else:
+                    msg += f"，可转写音频（{'→'.join(providers)}）"
+        return "ok", msg
+
+    def transcribe(self, url: str, *, provider: str = "auto", config=None) -> str:
+        """Download a YouTube video's audio and return its transcript.
+
+        Delegates to :func:`agent_reach.transcribe.transcribe`. Imported lazily
+        so the channel module stays cheap to import for users who never
+        transcribe.
+        """
+        from agent_reach.transcribe import transcribe as _transcribe
+
+        return _transcribe(url, provider=provider, config=config)
+