Add Docker setup, .env.example, updated .gitignore/CHANGELOG and ADRs 004-007 + arc42 template

backend/playout/Dockerfile

@@ -0,0 +1,25 @@
+FROM alpine:3.20
+
+# Install FFmpeg, curl for health checks, and basic tools
+RUN apk add --no-cache \
+    ffmpeg \
+    curl \
+    bash
+
+WORKDIR /app
+
+# Copy playout scripts and configuration
+COPY src/ /app/src/
+COPY config/ /app/config/
+COPY *.sh /app/
+
+RUN chmod +x /app/*.sh
+
+# Create directories for playlist and HLS output
+RUN mkdir -p /app/playlist /app/hls
+
+# Expose HLS directory (will be served by nginx)
+VOLUME ["/app/hls"]
+
+# Default command runs the playout loop
+CMD ["./start-playout.sh"]