Phase 3: banger kernel import bridges make-*-kernel.sh output

`banger kernel import <name> --from <dir>` copies a staged kernel
bundle into the local catalog. <dir> is the output of
`make void-kernel` or `make alpine-kernel` (build/manual/void-kernel/
or build/manual/alpine-kernel/).

kernelcat.DiscoverPaths locates artifacts under <dir>:
 1. Prefers metadata.json (written by make-void-kernel.sh).
 2. Falls back to globbing: boot/vmlinux-* or vmlinuz-* (Alpine
    fallback), boot/initramfs-*, lib/modules/<latest>.

The daemon's KernelImport copies kernel + optional initrd via
system.CopyFilePreferClone and modules via system.CopyDirContents
(no-sudo mode — catalog lives under ~/.local/state), computes SHA256
over the kernel, and writes the manifest via kernelcat.WriteLocal.

While wiring this up, fixed a latent bug in system.CopyDirContents:
filepath.Join(sourceDir, ".") silently drops the trailing dot, so
`cp -a source source/contents target/` was copying the whole source
directory (including its basename) instead of just its contents.
Replaced the join with a manual "/." suffix. imagemgr.StageBootArtifacts
(the only existing caller) silently benefits.

scripts/register-void-image.sh and scripts/register-alpine-image.sh
are rewritten to use `banger kernel import … && banger image register
--kernel-ref …` instead of the find-and-pass-paths dance. Preserves
the same user-facing commands and env vars.

Tests cover: metadata.json preference, glob fallback, Alpine vmlinuz
fallback, kernel-missing error, round-trip copy into the catalog, and
the --from required flag.

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

internal/cli/banger.go

@@ -1599,10 +1599,45 @@ func newKernelCommand() *cobra.Command {
 		newKernelListCommand(),
 		newKernelShowCommand(),
 		newKernelRmCommand(),
+		newKernelImportCommand(),
 	)
 	return cmd
 }
 
+func newKernelImportCommand() *cobra.Command {
+	var params api.KernelImportParams
+	cmd := &cobra.Command{
+		Use:   "import <name>",
+		Short: "Import a kernel bundle produced by scripts/make-*-kernel.sh",
+		Long:  "Copy the kernel, optional initrd, and optional modules directory from <from> into the local kernel catalog keyed by <name>. <from> is usually build/manual/void-kernel or build/manual/alpine-kernel.",
+		Args:  exactArgsUsage(1, "usage: banger kernel import <name> --from <dir>"),
+		RunE: func(cmd *cobra.Command, args []string) error {
+			params.Name = args[0]
+			if strings.TrimSpace(params.FromDir) == "" {
+				return errors.New("--from <dir> is required")
+			}
+			abs, err := filepath.Abs(params.FromDir)
+			if err != nil {
+				return err
+			}
+			params.FromDir = abs
+			layout, _, err := ensureDaemon(cmd.Context())
+			if err != nil {
+				return err
+			}
+			result, err := rpc.Call[api.KernelShowResult](cmd.Context(), layout.SocketPath, "kernel.import", params)
+			if err != nil {
+				return err
+			}
+			return printJSON(cmd.OutOrStdout(), result.Entry)
+		},
+	}
+	cmd.Flags().StringVar(&params.FromDir, "from", "", "directory produced by make-*-kernel.sh (e.g. build/manual/void-kernel)")
+	cmd.Flags().StringVar(&params.Distro, "distro", "", "distribution label stored in the manifest (e.g. void, alpine)")
+	cmd.Flags().StringVar(&params.Arch, "arch", "", "architecture label stored in the manifest (e.g. x86_64)")
+	return cmd
+}
+
 func newKernelListCommand() *cobra.Command {
 	return &cobra.Command{
 		Use:   "list",