Point the "Online Python Console" link to a working console (#185)

Trinket shut down in August 2026. The sidebar link now opens a Python playground with NumPy, SciPy and Matplotlib.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

Author: KevinSpek

_templates/navigation.html

@@ -16,6 +16,6 @@
         </a>
         <a target="_blank" href="https://github.com/777arc/PySDR">GitHub Link</a>
     </li>
-    <li class="toctree-l1"><a target="_blank" href="https://trinket.io/embed/python3"><img width="15px" height="12px" src="https://pysdr.org/_static/python.svg"> Online Python Console</a></li>
+    <li class="toctree-l1"><a target="_blank" href="https://coddy.tech/playground/matplotlib"><img width="15px" height="12px" src="https://pysdr.org/_static/python.svg"> Online Python Console</a></li>
     <li class="toctree-l1"><a target="_blank" href="https://www.paypal.com/donate/?hosted_button_id=FH3LQCJRUVPWL"><img width="15px" height="12px" src="https://pysdr.org/_static/donate.svg"> One-time Donation</a></li>
 </ul>