Shut down WebSocket socket to prevent Werkzeug HTTP response leak

After a WebSocket handler exits, flask-sock returns a Response to
Werkzeug which writes "HTTP/1.1 200 OK..." on the still-open socket.
Browsers see these HTTP bytes as a malformed WebSocket frame, causing
"Invalid frame header".

Now the handler explicitly closes the raw TCP socket after the
WebSocket close handshake, so Werkzeug's write harmlessly fails.
Applied to both waterfall and audio WebSocket handlers.

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

routes/waterfall_websocket.py

@@ -2,6 +2,7 @@
 
 import json
 import queue
+import socket
 import subprocess
 import threading
 import time
@@ -348,4 +349,20 @@ def init_waterfall_websocket(app: Flask):
                 unregister_process(iq_process)
             if claimed_device is not None:
                 app_module.release_sdr_device(claimed_device)
+            # Complete WebSocket close handshake, then shut down the
+            # raw socket so Werkzeug cannot write its HTTP 200 response
+            # on top of the WebSocket stream (which browsers see as
+            # "Invalid frame header").
+            try:
+                ws.close()
+            except Exception:
+                pass
+            try:
+                ws.sock.shutdown(socket.SHUT_RDWR)
+            except Exception:
+                pass
+            try:
+                ws.sock.close()
+            except Exception:
+                pass
             logger.info("WebSocket waterfall client disconnected")