fix(pipeline): cancel sibling loops on failure (TaskGroup, no close-during-use)

Pipeline.run() used asyncio.gather, so if one loop raised, the failing
coroutine propagated while the sibling loops kept running detached; aclose()
in the finally then closed a source/stt out from under a still-live loop.
Switch to asyncio.TaskGroup so a failing loop cancels+awaits the siblings
before teardown. Add a regression test asserting an error in the conversation
loop cancels the perception loop and still closes every source.

wsai/pipeline.py

@@ -102,9 +102,16 @@ class Pipeline:
 
     # -- lifecycle --------------------------------------------------------- #
     async def run(self) -> None:
-        loops = [self._perceive(), self._listen_voice(), self._listen_text()]
+        # A TaskGroup (not bare gather) so that if ONE loop raises, the others
+        # are cancelled and awaited before teardown. With plain gather the
+        # failing loop propagated while the siblings kept running detached, and
+        # aclose() in the finally then closed a source/stt out from under a
+        # still-live loop (close-during-use).
         try:
-            await asyncio.gather(*loops)
+            async with asyncio.TaskGroup() as tg:
+                tg.create_task(self._perceive())
+                tg.create_task(self._listen_voice())
+                tg.create_task(self._listen_text())
         finally:
             await self.aclose()