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/create-rpi-image.sh

@@ -83,9 +83,38 @@ type=0FC63DAF-8483-4772-8E79-3D69D8477DE4, name="Data"
 EOF
 
 # --- Set up loop device ---
-LOOP=$(losetup --show -fP "$IMG_OUTPUT")
+LOOP=$(losetup --show -f "$IMG_OUTPUT")
 echo "==> Loop device: $LOOP"
 
+# Use kpartx for reliable partition device nodes (works in Docker/containers)
+USE_KPARTX=false
+if [ ! -b "${LOOP}p1" ]; then
+    if command -v kpartx >/dev/null 2>&1; then
+        kpartx -a "$LOOP"
+        USE_KPARTX=true
+        sleep 1
+        LOOP_NAME=$(basename "$LOOP")
+        P1="/dev/mapper/${LOOP_NAME}p1"
+        P2="/dev/mapper/${LOOP_NAME}p2"
+        P3="/dev/mapper/${LOOP_NAME}p3"
+        P4="/dev/mapper/${LOOP_NAME}p4"
+    else
+        # Retry with -P flag
+        losetup -d "$LOOP"
+        LOOP=$(losetup --show -fP "$IMG_OUTPUT")
+        sleep 1
+        P1="${LOOP}p1"
+        P2="${LOOP}p2"
+        P3="${LOOP}p3"
+        P4="${LOOP}p4"
+    fi
+else
+    P1="${LOOP}p1"
+    P2="${LOOP}p2"
+    P3="${LOOP}p3"
+    P4="${LOOP}p4"
+fi
+
 MNT_CTL=$(mktemp -d)
 MNT_BOOTA=$(mktemp -d)
 MNT_BOOTB=$(mktemp -d)
@@ -96,22 +125,25 @@ cleanup() {
     umount "$MNT_BOOTA" 2>/dev/null || true
     umount "$MNT_BOOTB" 2>/dev/null || true
     umount "$MNT_DATA" 2>/dev/null || true
+    if [ "$USE_KPARTX" = true ]; then
+        kpartx -d "$LOOP" 2>/dev/null || true
+    fi
     losetup -d "$LOOP" 2>/dev/null || true
     rm -rf "$MNT_CTL" "$MNT_BOOTA" "$MNT_BOOTB" "$MNT_DATA" 2>/dev/null || true
 }
 trap cleanup EXIT
 
 # --- Format partitions ---
-mkfs.vfat -F 32 -n KSOLOCTL "${LOOP}p1"
-mkfs.vfat -F 32 -n KSOLOA "${LOOP}p2"
-mkfs.vfat -F 32 -n KSOLOB "${LOOP}p3"
-mkfs.ext4 -q -L KSOLODATA "${LOOP}p4"
+mkfs.vfat -F 32 -n KSOLOCTL "$P1"
+mkfs.vfat -F 32 -n KSOLOA "$P2"
+mkfs.vfat -F 32 -n KSOLOB "$P3"
+mkfs.ext4 -q -L KSOLODATA "$P4"
 
 # --- Mount all partitions ---
-mount "${LOOP}p1" "$MNT_CTL"
-mount "${LOOP}p2" "$MNT_BOOTA"
-mount "${LOOP}p3" "$MNT_BOOTB"
-mount "${LOOP}p4" "$MNT_DATA"
+mount "$P1" "$MNT_CTL"
+mount "$P2" "$MNT_BOOTA"
+mount "$P3" "$MNT_BOOTB"
+mount "$P4" "$MNT_DATA"
 
 # --- Boot Control Partition (KSOLOCTL) ---
 echo "    Writing autoboot.txt..."