Relocate bundled demo sources into bundled-demos/demo/

Mirror bundled-lib/ by keeping manifest.json at the bundle root and
shipping sample .py files from a demo/ subdirectory.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/static/bundled-demos/demo/main.py

@@ -0,0 +1,3 @@
+"""Sample script — runs in the browser under Pyodide."""
+
+print("Hello from Pyodide")