Add Dockerfile, compose file and Gitea Actions workflow

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

Dockerfile

@@ -0,0 +1,12 @@
+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 ./
+USER app
+VOLUME /data
+EXPOSE 8080
+HEALTHCHECK --interval=30s --timeout=5s --retries=3 \
+  CMD python -c "import urllib.request,os;urllib.request.urlopen('http://127.0.0.1:%s/login'%os.environ['PORT'])" || exit 1
+CMD ["python", "server.py", "serve"]