Add Docker Compose and Podman support for containerized deployment

Adds Dockerfile, docker-compose.yml, and .dockerignore to enable
running ADS-Bit in a container with host networking for LAN receiver
auto-scanning. Bind mounts persist config, sprites, and backgrounds
across container recreation. Updates README with usage instructions.

Closes #4

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,21 @@
+FROM python:3.11-slim
+
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends gcc python3-dev && \
+    rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt && \
+    apt-get purge -y gcc python3-dev && \
+    apt-get autoremove -y && \
+    rm -rf /var/lib/apt/lists/*
+
+COPY . .
+
+EXPOSE 2001
+
+ENV PYTHONUNBUFFERED=1
+
+CMD ["python3", "server.py"]