test: add minimal Gradio app for Space diagnosis

app_test.py

@@ -0,0 +1,19 @@
+#!/usr/bin/env python3
+"""
+Minimal Gradio test to verify Space deployment
+"""
+import gradio as gr
+
+def test_function(text):
+    return f"Echo: {text}"
+
+with gr.Blocks(title="FBMC Test") as demo:
+    gr.Markdown("# Minimal Test App")
+    with gr.Row():
+        input_text = gr.Textbox(label="Input")
+        output_text = gr.Textbox(label="Output")
+    btn = gr.Button("Test")
+    btn.click(fn=test_function, inputs=input_text, outputs=output_text)
+
+if __name__ == "__main__":
+    demo.launch(server_name="0.0.0.0", server_port=7860)