dashboard: env-configurable port, plus ?demo=1 preview mode

flockyou.py: bind host and listen port both read from env
(FLOCKYOU_HOST / FLOCKYOU_PORT, defaulting to 0.0.0.0:5000). Was a
hardcoded :5000 before, which collides with other Flask projects on
the same dev box — now you can run side-by-side instances or bind
to localhost only.

index.html: ?demo=1 query param seeds the dashboard with eight
synthetic detections covering every visual state (live wildcard-probe,
addr2, addr1 with/without GPS, replay/FLASH with/without GPS, replay/
RAM × 2) and reveals the device command toolbar so the polished layout
is browseable without flashing real hardware. Purely a front-end mock
— the command buttons still hit the real /api/flock/* endpoints, so
clicking them in demo mode produces the actual "device not connected"
error toast (that error path is itself part of the UI worth seeing).
Self-contained: a single initDemoMode() function gated on the query
param, called once at the end of DOMContentLoaded.

api/README.md: both features documented under Quick start so they're
discoverable without reading the source.

api/flockyou.py

@@ -1763,12 +1763,15 @@ if __name__ == '__main__':
     heartbeat_thread = threading.Thread(target=send_heartbeat, daemon=True)
     heartbeat_thread.start()
     
+    host = os.environ.get('FLOCKYOU_HOST', '0.0.0.0')
+    port = int(os.environ.get('FLOCKYOU_PORT', '5000'))
+
     print("Starting Flock You API server...")
-    print("Server will be available at: http://localhost:5000")
+    print(f"Server will be available at: http://localhost:{port}")
     print("Press Ctrl+C to stop the server")
-    
+
     try:
-        socketio.run(app, debug=False, host='0.0.0.0', port=5000, allow_unsafe_werkzeug=True)
+        socketio.run(app, debug=False, host=host, port=port, allow_unsafe_werkzeug=True)
     except KeyboardInterrupt:
         print("\nShutting down server...")
         # Clean up connections