Test docker image, basic functionality

Dockerfile

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+FROM python:3.13-slim
+
+# Install FFmpeg and dependencies (gosu will be downloaded separately)
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends ffmpeg ca-certificates wget gpg && \
+    apt-get clean && \
+    rm -rf /var/lib/apt/lists/*
+
+# Install gosu (lightweight tool for dropping privileges)
+RUN set -eux; \
+    dpkgArch="$(dpkg --print-architecture | awk -F- '{ print $NF }')"; \
+    wget -O /usr/local/bin/gosu "https://github.com/tianon/gosu/releases/download/1.17/gosu-$dpkgArch"; \
+    wget -O /usr/local/bin/gosu.asc "https://github.com/tianon/gosu/releases/download/1.17/gosu-$dpkgArch.asc"; \
+    export GNUPGHOME="$(mktemp -d)"; \
+    gpg --batch --keyserver hkps://keys.openpgp.org --recv-keys B42F6819007F00F88E364FD4036A9C25BF357DD4; \
+    gpg --batch --verify /usr/local/bin/gosu.asc /usr/local/bin/gosu; \
+    gpgconf --kill all; \
+    rm -rf "$GNUPGHOME" /usr/local/bin/gosu.asc; \
+    chmod +x /usr/local/bin/gosu; \
+    gosu --version
+
+# Set Python environment variables
+ENV PYTHONDONTWRITEBYTECODE=1 \
+    PYTHONUNBUFFERED=1
+
+# Set working directory
+WORKDIR /app
+
+# Copy package metadata and source code
+COPY setup.py pyproject.toml README.md ./
+COPY audio_splitter/ ./audio_splitter/
+
+# Install the package
+RUN pip install --no-cache-dir .
+
+# Create a non-root user with UID 1000
+RUN addgroup --system --gid 1000 appgroup && \
+    adduser --system --uid 1000 --ingroup appgroup appuser
+
+# Change ownership of /app to the container user (so it can write there if needed)
+RUN chown -R appuser:appgroup /app
+
+# Copy the entrypoint script
+COPY docker-entrypoint.sh /usr/local/bin/docker-entrypoint.sh
+RUN chmod +x /usr/local/bin/docker-entrypoint.sh
+
+# Set the entrypoint
+ENTRYPOINT ["/usr/local/bin/docker-entrypoint.sh"]
+
+# Default command (shows help if no arguments)
+CMD ["audio_splitter", "--help"]