feat: convert to multi-stage build to reduce image size (closes #14)

Dockerfile

@@ -1,4 +1,23 @@
 FROM debian:bookworm-slim
+# NOTE:
+# linux-sysmonitor is a Bash-based application, so there are no compiled build artifacts.
+# This multi-stage build demonstrates the builder/runtime pattern. The builder prepares
+# the application, while the runtime contains only the files and dependencies required
+# to execute the script.
+
+FROM debian:bookworm-slim AS builder
+
+
+WORKDIR /app
+
+COPY linux-sysmonitor/ . 
+RUN chmod +x health-check.sh
+
+FROM debian:bookworm-slim
+
+WORKDIR /app
+
+COPY --from=builder /app/health-check.sh .
 
 
 WORKDIR /app
@@ -8,7 +27,4 @@ RUN apt-get update && apt-get install -y \
     iputils-ping \
     iproute2 \
     bash && rm -rf /var/lib/apt/lists/*
-
-COPY linux-sysmonitor/ . 
-RUN chmod +x health-check.sh
 ENTRYPOINT [ "./health-check.sh" ]