Dockerfile: COPY assets/ and social-banner.html into the prod image

The modular CSS/JS split (39a61da) moved every stylesheet and per-section
script out of inline demo.html into assets/, but the Dockerfile never
gained a `COPY assets/`, so each rebuild has shipped a prod image with
no stylesheets and no JS modules — the page renders unstyled and inert,
every /assets/* URL 404s. social-banner.html (added in b64beb5) was in
the same boat.

Add both to the COPY list. No changes to runtime / requirements.

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

Dockerfile

@@ -5,9 +5,14 @@ WORKDIR /app
 COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
-COPY app.py index.html demo.html ./
+COPY app.py index.html demo.html social-banner.html ./
 COPY data/ ./data/
 COPY img/ ./img/
+# Modular CSS/JS for demo.html. demo.html links these by relative URL
+# (/assets/styles/*.css, /assets/js/**/*.js) and app.py mounts the
+# directory as static; without this COPY the prod image serves the
+# HTML but every stylesheet and module 404s.
+COPY assets/ ./assets/
 
 ENV PORT=7860
 EXPOSE 7860