Add Dockerfile

Dockerfile

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+FROM --platform=$BUILDPLATFORM golang:alpine AS builder
+
+ARG TARGETOS
+ARG TARGETARCH
+
+ENV GONOPROXY="none" \
+    CGO_ENABLED=0 \
+    GOFLAGS="-mod=readonly -trimpath -modcacherw"
+
+# git is needed for go modules, ca-certificates for system CAs.
+RUN apk add --no-cache git ca-certificates && update-ca-certificates
+
+WORKDIR /src
+
+RUN mkdir -p /output
+
+# --- Create Non-Root User ---
+RUN addgroup --gid "1337" app && \
+    adduser --disabled-password --gecos "" --no-create-home --uid 1337 --ingroup app --shell /bin/false app && \
+    cat /etc/passwd | grep app > "/etc/passwd_app" && \
+    cat /etc/group | grep app > "/etc/group_app"
+
+COPY go.mod go.sum /src/
+RUN go mod download
+
+# === CACHE BREAKS HERE ON CODE CHANGE ===
+# --- Copy Source Code ---
+COPY . .
+
+RUN --mount=type=cache,target=/root/.cache/go-build \
+    --mount=type=cache,target=/go/pkg/mod \
+    GOOS=${TARGETOS} GOARCH=${TARGETARCH} \
+    go build -tags timetzdata -buildvcs=false \
+    -ldflags "-s -w" \
+    -o /output/sn
+
+FROM scratch
+
+# Copy minimal user and group files for the non-root user
+# This is necessary because scratch has no users defined
+COPY --from=builder /etc/passwd_app /etc/passwd
+COPY --from=builder /etc/group_app /etc/group
+
+## /server executable
+COPY --from=builder --chown=1337:1337 /output/ /app/
+COPY --from=builder --chown=1337:1337 /etc/ssl/certs/ca-certificates.crt /app/certs/
+
+# Set SSL cert environment variables
+ENV SSL_CERT_DIR="/app/certs" \
+    SSL_CERT_FILE="/app/certs/ca-certificates.crt"
+
+WORKDIR /app
+
+# --- Metadata & Security ---
+LABEL security.read-only-root-filesystem="true" \
+      security.non-root-user="1337" \
+      security.capabilities.drop="ALL"
+
+# Create and switch to non-root user
+USER 1337:1337
+
+# Expose port (documentation only - doesn't actually open ports)
+EXPOSE 8080
+
+# Use exec form to avoid shell and ensure proper signal handling
+ENTRYPOINT ["/app/sn"]