build: ship linux/arm64 binaries

goreleaser excluded linux/arm64 while building darwin/arm64, so ARM
Linux servers, Raspberry Pis, Graviton instances, and ARM CI runners had
no prebuilt binary. Nothing blocked it technically: the build is
CGO_ENABLED=0 and the image codecs run on wazero, a pure Go WASM
runtime, so there is no cgo toolchain to cross-compile.

Also drops the linux/arm64 guard added to install.sh earlier today.
That asset now exists, and leaving the guard would refuse to install on
a supported platform. All five published targets verified to build.

Author: frostybee

.goreleaser.yaml

@@ -19,8 +19,6 @@ builds:
     ignore:
       - goos: windows
         goarch: arm64
-      - goos: linux
-        goarch: arm64
 
 archives:
   - formats:

install.sh

@@ -29,15 +29,8 @@ detect_platform() {
       ;;
   esac
 
-  # goreleaser does not build linux/arm64, so fail with a usable message
-  # rather than letting the download 404.
-  if [ "$OS" = "linux" ] && [ "$ARCH" = "arm64" ]; then
-    echo "Error: no prebuilt binary for linux/arm64." >&2
-    echo "Install from source instead:" >&2
-    echo "  go install github.com/getsarde/sarde/cmd/sarde@latest" >&2
-    exit 1
-  fi
-
+  # windows/arm64 is the only combination goreleaser excludes, and this script
+  # never runs there (the OS check above already rejected it).
   echo "${OS}_${ARCH}"
 }