Add 'Reset demos' button to refresh canonical demo files

Existing accounts (including admin) seeded before new demos shipped
had no easy way to pull in the latest copies — the registration-time
seeder is intentionally non-destructive. The new badge action fetches
src/static/bundled-demos/manifest.json, confirms the overwrite, and
re-copies each canonical demo into code/. Open tabs of those files are
refreshed in place so the user sees the new content immediately.

src/static/bundled-demos/ ships the six canonical files plus the
manifest so this works in local mode and on a static-only host. The
Dockerfile now mirrors workspace/code/<demo>.py into bundled-demos/
during the image build, keeping the two locations in sync.

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

Dockerfile

@@ -15,6 +15,13 @@ COPY src ./src
 COPY lib ./lib
 RUN mkdir -p src/static/bundled-lib && cp -f lib/*.py src/static/bundled-lib/
 COPY workspace ./workspace
+# Mirror canonical demo files into the static bundle so the editor's
+# "Reset demos" button works from a static-only host too.
+RUN mkdir -p src/static/bundled-demos && \
+    for f in pattern_rainbow_demo.py pattern_twinkle_demo.py pattern_chase_demo.py \
+             adc_slider_demo.py pin_demo.py serial_demo.py; do \
+        cp -f "workspace/code/$f" "src/static/bundled-demos/$f"; \
+    done
 
 EXPOSE 8080