Add: serve loading page while Streamlit boots

start.sh

@@ -1,4 +1,42 @@
 #!/bin/bash
-# Start the scheduler in the background, then launch Streamlit
+# Serve loading page on 8501 while Streamlit boots on 8502,
+# then switch Streamlit to 8501 once ready.
+
 python scheduler.py &
-streamlit run streamlit_app.py --server.port=8501 --server.address=0.0.0.0
+
+# Start Streamlit on temp port 8502
+streamlit run streamlit_app.py --server.port=8502 --server.address=0.0.0.0 &
+STREAMLIT_PID=$!
+
+# Serve loading.html on 8501 while waiting
+python3 -c "
+import http.server, urllib.request, time, sys
+
+class Handler(http.server.BaseHTTPRequestHandler):
+    def do_GET(self):
+        self.send_response(200)
+        self.send_header('Content-type', 'text/html')
+        self.end_headers()
+        with open('/app/loading.html', 'rb') as f:
+            self.wfile.write(f.read())
+    def log_message(self, *args): pass
+
+server = http.server.HTTPServer(('0.0.0.0', 8501), Handler)
+server.timeout = 1
+
+# Poll until Streamlit on 8502 is healthy
+while True:
+    try:
+        urllib.request.urlopen('http://localhost:8502/_stcore/health', timeout=1)
+        break
+    except Exception:
+        server.handle_request()
+
+server.server_close()
+print('Streamlit ready — switching ports')
+"
+
+# Kill Streamlit on 8502, relaunch on 8501
+kill $STREAMLIT_PID 2>/dev/null
+wait $STREAMLIT_PID 2>/dev/null
+exec streamlit run streamlit_app.py --server.port=8501 --server.address=0.0.0.0