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/manifest.json

@@ -1,10 +1,11 @@
 {
   "files": [
-    "pattern_rainbow_demo.py",
-    "pattern_twinkle_demo.py",
-    "pattern_chase_demo.py",
-    "adc_slider_demo.py",
-    "pin_demo.py",
-    "serial_demo.py"
+    "demo/pattern_rainbow_demo.py",
+    "demo/pattern_twinkle_demo.py",
+    "demo/pattern_chase_demo.py",
+    "demo/adc_slider_demo.py",
+    "demo/pin_demo.py",
+    "demo/serial_demo.py",
+    "demo/aiohttp_fetch_demo.py"
   ]
 }