Split features/ into audio/, observability/, and rag/ subfolders

Extract focused example groups from the catch-all features/ folder:
- audio/: audio recording, background sound, sound effects
- observability/: observer, heartbeats, sentry metrics
- rag/: mem0, gemini-rag, gemini grounding metadata

Update README to document the new folders.

examples/observability/heartbeats.py

@@ -0,0 +1,43 @@
+#
+# Copyright (c) 2024-2026, Daily
+#
+# SPDX-License-Identifier: BSD 2-Clause License
+#
+
+import asyncio
+import sys
+
+from loguru import logger
+
+from pipecat.frames.frames import Frame
+from pipecat.pipeline.pipeline import Pipeline
+from pipecat.pipeline.runner import PipelineRunner
+from pipecat.pipeline.task import PipelineParams, PipelineTask
+from pipecat.processors.frame_processor import FrameDirection, FrameProcessor
+
+logger.remove(0)
+logger.add(sys.stderr, level="DEBUG")
+
+
+class NullProcessor(FrameProcessor):
+    async def process_frame(self, frame: Frame, direction: FrameDirection):
+        await super().process_frame(frame, direction)
+
+
+async def main():
+    """This test shows heartbeat monitoring.
+
+    A warning is dispalyed when heartbeats are not received within the
+    default (5 seconds) timeout.
+    """
+    pipeline = Pipeline([NullProcessor()])
+
+    task = PipelineTask(pipeline, params=PipelineParams(enable_heartbeats=True))
+
+    runner = PipelineRunner()
+
+    await runner.run(task)
+
+
+if __name__ == "__main__":
+    asyncio.run(main())