fix(01-05): expose a module-level `demo` for the Space runner

Third deploy (e3ebc72) built, imported and printed "Running on local URL", then
stopped the Node server and exited with RUNTIME_ERROR and no traceback. The Space
launches under gradio.utils.SpacesReloader, whose postrun() calls
`getattr(watch_module, demo_name)` on every reload check; with the Blocks living
only inside build_app() the module had no such attribute, which the log announced
as `GRADIO_HOT_RELOAD: Launching demo not found in __main__. Using 'demo'`.

build_app() stays, so tests keep building an independent app.

app.py

@@ -72,7 +72,7 @@ def _echo(text: str, slower: bool, history: str) -> tuple[str, str]:
 
 def build_app() -> gr.Blocks:
     """Build the Blocks app. Importable and callable from tests without launching."""
-    with gr.Blocks(title="Japanese Learning Avatar", fill_height=True) as demo:
+    with gr.Blocks(title="Japanese Learning Avatar", fill_height=True) as blocks:
         with gr.Row(equal_height=True):
             with gr.Column(scale=3, min_width=320):
                 VrmStage()
@@ -96,8 +96,20 @@ def build_app() -> gr.Blocks:
 
         send.click(_echo, [text_in, slower, transcript], [transcript, text_in])
         text_in.submit(_echo, [text_in, slower, transcript], [transcript, text_in])
-    return demo
+    return blocks
 
 
+# Module level, and named `demo`, because that is what the Space runner requires.
+# Hugging Face launches the app under gradio.utils.SpacesReloader, whose postrun() does
+# `getattr(watch_module, self.demo_name)` on every reload check. With the Blocks living
+# only inside build_app() there was no such attribute: the third deploy (e3ebc72) logged
+# `GRADIO_HOT_RELOAD: Launching demo not found in __main__. Using 'demo'`, printed its
+# "Running on local URL" line, and then stopped the Node server and exited - RUNTIME_ERROR
+# with no traceback. The factory is kept so tests can build an independent app.
+#
+# This is the one module-level object this file is allowed to own. It is the app itself,
+# not shared state: nothing mutates it per session.
+demo = build_app()
+
 if __name__ == "__main__":
-    build_app().launch()
+    demo.launch()