fix: wrap YouTubeTranscriptApi in run_in_executor with 30s timeout

The synchronous get_transcript() call was blocking the asyncio event
loop indefinitely, freezing the entire bot (including Telegram polling).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/scraper/exhaustive.py

@@ -469,12 +469,23 @@ class ExhaustiveScraper:
             return None, None
 
         video_id = match.group(1)
-        try:
-            transcript_list = YouTubeTranscriptApi.get_transcript(
+        loop = asyncio.get_event_loop()
+
+        def _fetch():
+            return YouTubeTranscriptApi.get_transcript(
                 video_id, languages=["en", "es", "en-US", "en-GB"]
             )
+
+        try:
+            transcript_list = await asyncio.wait_for(
+                loop.run_in_executor(None, _fetch),
+                timeout=30.0
+            )
             text = " ".join(t["text"] for t in transcript_list)
             return text, f"YouTube: {video_id}"
+        except asyncio.TimeoutError:
+            logger.warning("YouTube transcript timed out", video_id=video_id)
+            return None, None
         except NoTranscriptFound:
             return None, None
         except Exception as e: