fix(scraper): DDGS síncrono ya no bloquea el event loop

Las llamadas DDGS() en _seed_search y _seed_youtube eran síncronas y se
ejecutaban directamente en código async: durante cada búsqueda DDG el bot
entero (comandos de Telegram incluidos) quedaba congelado. Extraídas a
helpers sync (_ddg_text_sync/_ddg_videos_sync) ejecutados vía
run_in_executor. Sin cambios en queries ni procesamiento de resultados.

Verificado con mock de DDG lento (3s): peor parón del loop 52ms.

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

src/scraper/exhaustive.py

@@ -266,6 +266,21 @@ class ExhaustiveScraper:
             logger.warning("SearXNG failed", query=query, error=str(e))
             return []
 
+    # DDGS es síncrono (requests bloqueante por dentro): llamarlo directamente
+    # desde código async congela el event loop entero — bot de Telegram incluido —
+    # mientras dura la búsqueda. Estos helpers deben ejecutarse SIEMPRE vía
+    # run_in_executor.
+
+    @staticmethod
+    def _ddg_text_sync(query: str) -> list[dict]:
+        with DDGS() as ddgs:
+            return list(ddgs.text(query, max_results=settings.max_pages_per_search))
+
+    @staticmethod
+    def _ddg_videos_sync(query: str) -> list[dict]:
+        with DDGS() as ddgs:
+            return list(ddgs.videos(query, max_results=10))
+
     async def _seed_search(self):
         """SearXNG primary + DDG fallback per query"""
         queries = await self._generate_ddg_queries()
@@ -276,12 +291,10 @@ class ExhaustiveScraper:
             if not results:
                 logger.info("SearXNG vacío, usando DDG", query=query)
                 try:
-                    with DDGS() as ddgs:
-                        ddg_results = list(ddgs.text(
-                            query,
-                            max_results=settings.max_pages_per_search
-                        ))
-                    results = ddg_results
+                    loop = asyncio.get_running_loop()
+                    results = await loop.run_in_executor(
+                        None, self._ddg_text_sync, query
+                    )
                     logger.info("DDG fallback ok", query=query, results=len(results))
                 except Exception as e:
                     logger.warning("DDG fallback failed", query=query, error=str(e))
@@ -395,18 +408,18 @@ class ExhaustiveScraper:
     async def _seed_youtube(self):
         """Search YouTube via DDG for video transcripts"""
         try:
-            with DDGS() as ddgs:
-                results = list(ddgs.videos(
-                    f"{self.topic} documentary explanation",
-                    max_results=10
-                ))
-                for r in results:
-                    url = r.get("content", "")
-                    if "youtube.com" in url or "youtu.be" in url:
-                        await self.db.add_source(
-                            self.session_id, url, "youtube", depth=0,
-                            title=r.get("title")
-                        )
+            loop = asyncio.get_running_loop()
+            results = await loop.run_in_executor(
+                None, self._ddg_videos_sync,
+                f"{self.topic} documentary explanation"
+            )
+            for r in results:
+                url = r.get("content", "")
+                if "youtube.com" in url or "youtu.be" in url:
+                    await self.db.add_source(
+                        self.session_id, url, "youtube", depth=0,
+                        title=r.get("title")
+                    )
         except Exception as e:
             logger.warning("YouTube seed failed", error=str(e))