Fix: add ctrl+c signal for better exit (#5469)

### What problem does this PR solve?

This patch add signal for ctrl + c that can exit the code friendly
cause code base use thread daemon can not exit friendly for being
started.

how to reproduce
1. docker-compose -f docker/docker-compose-base.yml up
2. other window `bash docker/launch_backend_service.sh`
3. stop 1 first
4. try to stop 2 then two thread can not exit which must use `kill pid`

This patch fix it 
and should fix most the related issues in the `issues`

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

---------

Signed-off-by: yihong0618 <zouzou0208@gmail.com>

rag/svr/task_executor.py

@@ -754,12 +754,33 @@ def main():
     if TRACE_MALLOC_ENABLED:
         start_tracemalloc_and_snapshot(None, None)
 
+    # Create an event to signal the background thread to exit
+    stop_event = threading.Event()
+    
     background_thread = threading.Thread(target=report_status)
     background_thread.daemon = True
     background_thread.start()
+ 
+    # Handle SIGINT (Ctrl+C)
+    def signal_handler(sig, frame):
+        logging.info("Received Ctrl+C, shutting down gracefully...")
+        stop_event.set()
+        # Give the background thread time to clean up
+        if background_thread.is_alive():
+            background_thread.join(timeout=5)
+        logging.info("Exiting...")
+        sys.exit(0)
 
-    while True:
-        handle_task()
+    signal.signal(signal.SIGINT, signal_handler)
+
+    try:
+        while not stop_event.is_set():
+            handle_task()
+    except KeyboardInterrupt:
+        logging.info("Interrupted by keyboard, shutting down...")
+        stop_event.set()
+        if background_thread.is_alive():
+            background_thread.join(timeout=5)
 
 if __name__ == "__main__":
     main()