Offline downloads, service worker, iOS audio unlock fix

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

Dockerfile

@@ -3,7 +3,7 @@ FROM python:3.13-slim
 ENV PYTHONUNBUFFERED=1 DATA_DIR=/data PORT=8080
 RUN useradd --system --uid 10001 --home /app app && mkdir /data && chown app /data
 WORKDIR /app
-COPY server.py index.html admin.html manifest.webmanifest icon-180.png icon-192.png icon-512.png ./
+COPY server.py index.html admin.html manifest.webmanifest sw.js icon-180.png icon-192.png icon-512.png ./
 USER app
 VOLUME /data
 EXPOSE 8080