fix: use pre-built golangci-lint binary instead of go install

go install fails in alpine Docker builder because the linker (ld) is not
available. Download the official pre-built binary with SHA256 verification
instead. Supports both amd64 and arm64 architectures.

Fixes #126

Dockerfile

@@ -4,8 +4,20 @@ FROM golang@sha256:f6751d823c26342f9506c03797d2527668d095b0a15f1862cddb4d927a7a4
 
 RUN apk add --no-cache git make gcc musl-dev
 
-# Install golangci-lint v2
+# Install golangci-lint v2 (pre-built binary — go install fails in alpine due to missing linker)
-RUN go install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@5d1e709b7be35cb2025444e19de266b056b7b7ee # v2.10.1
+RUN set -e; \
+    GOLANGCI_VERSION="2.10.1"; \
+    case "$(uname -m)" in \
+        x86_64)  ARCH="amd64"; SHA256="dfa775874cf0561b404a02a8f4481fc69b28091da95aa697259820d429b09c99" ;; \
+        aarch64) ARCH="arm64"; SHA256="6652b42ae02915eb2f9cb2a2e0cac99514c8eded8388d88ae3e06e1a52c00de8" ;; \
+        *) echo "unsupported arch: $(uname -m)" >&2; exit 1 ;; \
+    esac; \
+    wget -q -O /tmp/golangci-lint.tar.gz \
+        "https://github.com/golangci/golangci-lint/releases/download/v${GOLANGCI_VERSION}/golangci-lint-${GOLANGCI_VERSION}-linux-${ARCH}.tar.gz"; \
+    echo "${SHA256}  /tmp/golangci-lint.tar.gz" | sha256sum -c -; \
+    tar -xzf /tmp/golangci-lint.tar.gz -C /usr/local/bin --strip-components=1 "golangci-lint-${GOLANGCI_VERSION}-linux-${ARCH}/golangci-lint"; \
+    rm /tmp/golangci-lint.tar.gz; \
+    golangci-lint version
 RUN go install golang.org/x/tools/cmd/goimports@009367f5c17a8d4c45a961a3a509277190a9a6f0 # v0.42.0
 
 WORKDIR /src