Switch to port 9000, and post a redirection notice at port 8000. This avoids a port conflicts since port 8000 is often used by other servers, and hopefully avoids a common source of new-user issues in the future

old_port_main.py

@@ -0,0 +1,20 @@
+from fastapi import FastAPI
+from fastapi.responses import HTMLResponse
+
+app = FastAPI()
+
+@app.get('/', response_class=HTMLResponse)
+def read_root():
+    return '''
+    <style>
+    body {
+        font-family: Arial;
+        font-size: 11pt;
+    }
+    </style>
+    <h4>The UI has moved to <a href="http://localhost:9000">http://localhost:9000</a>. The current address that you used (ending with :8000) will be removed in the future, so please use <a href="http://localhost:9000">http://localhost:9000</a> going ahead (and in any bookmarks you've saved).</h4>
+
+    <h3>Why has the address changed?</h3>
+    <p>The previously used port (8000) is often used by other servers, which results in port conflicts. So the project's port number has been changed, while the project is still young. Otherwise port-conflicts with 8000 will be a common source of new-user issues in the future.</p>
+    <p>Sorry about this, and apologies for the inconvenience :)</p>
+    '''