feat: Implement multi-stage Docker build for releases, reusing pre-built artifacts from CI and updating documentation.

Dockerfile

@@ -15,12 +15,37 @@ RUN go mod download
 COPY . .
 RUN CGO_ENABLED=0 GOOS=${TARGETOS} GOARCH=${TARGETARCH} go build -o /out/ds2api ./cmd/ds2api
 
-FROM debian:bookworm-slim
+FROM debian:bookworm-slim AS runtime-base
 WORKDIR /app
 RUN apt-get update && apt-get install -y --no-install-recommends ca-certificates wget && rm -rf /var/lib/apt/lists/*
+
+FROM runtime-base AS runtime-from-source
 COPY --from=go-builder /out/ds2api /usr/local/bin/ds2api
 COPY --from=go-builder /app/sha3_wasm_bg.7b9ca65ddd.wasm /app/sha3_wasm_bg.7b9ca65ddd.wasm
 COPY --from=go-builder /app/config.example.json /app/config.example.json
 COPY --from=webui-builder /app/static/admin /app/static/admin
+
+FROM runtime-base AS runtime-from-dist
+ARG TARGETARCH
+COPY dist/docker-input/linux_amd64.tar.gz /tmp/ds2api_linux_amd64.tar.gz
+COPY dist/docker-input/linux_arm64.tar.gz /tmp/ds2api_linux_arm64.tar.gz
+RUN set -eux; \
+    case "${TARGETARCH}" in \
+      amd64) ARCHIVE="/tmp/ds2api_linux_amd64.tar.gz" ;; \
+      arm64) ARCHIVE="/tmp/ds2api_linux_arm64.tar.gz" ;; \
+      *) echo "unsupported TARGETARCH: ${TARGETARCH}" >&2; exit 1 ;; \
+    esac; \
+    tar -xzf "${ARCHIVE}" -C /tmp; \
+    PKG_DIR="$(find /tmp -maxdepth 1 -type d -name "ds2api_*_linux_${TARGETARCH}" | head -n1)"; \
+    test -n "${PKG_DIR}"; \
+    install -Dm755 "${PKG_DIR}/ds2api" /usr/local/bin/ds2api; \
+    install -Dm644 "${PKG_DIR}/sha3_wasm_bg.7b9ca65ddd.wasm" /app/sha3_wasm_bg.7b9ca65ddd.wasm; \
+    install -Dm644 "${PKG_DIR}/config.example.json" /app/config.example.json; \
+    mkdir -p /app/static; \
+    cp -R "${PKG_DIR}/static/admin" /app/static/admin; \
+    rm -rf /tmp/ds2api_* /tmp/ds2api_linux_amd64.tar.gz /tmp/ds2api_linux_arm64.tar.gz
+
 EXPOSE 5001
 CMD ["/usr/local/bin/ds2api"]
+
+FROM runtime-from-source AS final