fix: complete ARM64 RPi build pipeline

- fetch-components.sh: download ARM64 KubeSolo binary (kubesolo-arm64)
- inject-kubesolo.sh: use arch-specific binaries for KubeSolo, cloud-init,
  and update agent; detect KVER from custom kernel when rootfs has none;
  cross-arch module resolution via find fallback when modprobe fails
- create-rpi-image.sh: kpartx support for Docker container builds
- Makefile: rootfs-arm64 depends on build-cross, includes pack-initramfs

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

build/scripts/fetch-components.sh

@@ -51,6 +51,39 @@ if [ "$FETCH_ARCH" = "arm64" ]; then
     echo "==> Fetching RPi firmware..."
     "$SCRIPT_DIR/fetch-rpi-firmware.sh"
 
+    # Download ARM64 KubeSolo binary
+    KUBESOLO_VERSION="${KUBESOLO_VERSION:-v1.1.0}"
+    KUBESOLO_BIN_ARM64="$CACHE_DIR/kubesolo-arm64"
+    if [ -f "$KUBESOLO_BIN_ARM64" ]; then
+        echo "==> KubeSolo ARM64 binary already cached: $KUBESOLO_BIN_ARM64"
+    else
+        echo "==> Downloading KubeSolo ${KUBESOLO_VERSION} (arm64)..."
+        BIN_URL="https://github.com/portainer/kubesolo/releases/download/${KUBESOLO_VERSION}/kubesolo-${KUBESOLO_VERSION}-linux-arm64-musl.tar.gz"
+        BIN_URL_FALLBACK="https://github.com/portainer/kubesolo/releases/download/${KUBESOLO_VERSION}/kubesolo-${KUBESOLO_VERSION}-linux-arm64.tar.gz"
+        TEMP_DIR=$(mktemp -d)
+        echo "    URL: $BIN_URL"
+        if curl -fSL "$BIN_URL" -o "$TEMP_DIR/kubesolo.tar.gz" 2>/dev/null; then
+            echo "    Downloaded musl variant (arm64)"
+        elif curl -fSL "$BIN_URL_FALLBACK" -o "$TEMP_DIR/kubesolo.tar.gz" 2>/dev/null; then
+            echo "    Downloaded glibc variant (arm64 fallback)"
+        else
+            echo "ERROR: Failed to download KubeSolo ARM64 from GitHub."
+            rm -rf "$TEMP_DIR"
+            exit 1
+        fi
+        tar -xzf "$TEMP_DIR/kubesolo.tar.gz" -C "$TEMP_DIR"
+        FOUND_BIN=$(find "$TEMP_DIR" -name "kubesolo" -type f ! -name "*.tar.gz" | head -1)
+        if [ -z "$FOUND_BIN" ]; then
+            echo "ERROR: Could not find kubesolo binary in extracted archive"
+            rm -rf "$TEMP_DIR"
+            exit 1
+        fi
+        cp "$FOUND_BIN" "$KUBESOLO_BIN_ARM64"
+        chmod +x "$KUBESOLO_BIN_ARM64"
+        rm -rf "$TEMP_DIR"
+        echo "==> KubeSolo ARM64 binary: $KUBESOLO_BIN_ARM64 ($(du -h "$KUBESOLO_BIN_ARM64" | cut -f1))"
+    fi
+
     # Skip x86_64 ISO and TCZ downloads for ARM64
     echo ""
     echo "==> ARM64 fetch complete."