cli: rewrite help text for AI-driven discovery

Frontier models tend to discover a CLI by running --help, scanning
the Long description, and inferring the dominant workflow from the
examples. Today's banger help reads like a man page index — every
verb has a one-line Short and nothing else. This rewrites the
groups (banger, vm, vm workspace, image, kernel, system,
ssh-config) so each landing page answers "what is this for, what's
the 80% command, what comes next" in three to ten lines, with
runnable examples.

Also disambiguates the near-twin lifecycle commands so a model
reading the subcommand index can tell stop/kill/delete apart at a
glance:

  start    Start a stopped VM
  stop     Stop a running VM gracefully
  restart  Stop then start a VM
  kill     Force-kill a VM (use when 'vm stop' hangs)
  delete   Stop a VM and remove its disks (irreversible)

vm create / vm ssh / vm logs / vm show pick up Long descriptions
and examples for the same reason. No behaviour changes; help text
only.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/cli/commands_kernel.go

@@ -15,8 +15,31 @@ import (
 func (d *deps) newKernelCommand() *cobra.Command {
 	cmd := &cobra.Command{
 		Use:   "kernel",
-		Short: "Manage the local kernel catalog",
-		RunE:  helpNoArgs,
+		Short: "Pull and manage Firecracker-compatible kernels",
+		Long: strings.TrimSpace(`
+Banger boots guests with a separate kernel artifact (vmlinux, plus
+optional initrd + modules). Kernels are tracked by name in a local
+catalog so multiple images can share one.
+
+Most users never run these commands directly: 'banger image pull'
+auto-pulls the kernel referenced by the catalog entry. Use these
+commands when you want to inspect what's installed, switch a VM to
+a different kernel via 'image register --kernel-ref', or import a
+kernel built locally with scripts/make-*-kernel.sh.
+
+Subcommands:
+  pull       download a cataloged kernel by name
+  list       show what's installed (or --available for the catalog)
+  show       inspect one entry as JSON
+  rm         remove a local kernel
+  import     register a kernel built from scripts/make-*-kernel.sh
+`),
+		Example: strings.TrimSpace(`
+  banger kernel list --available
+  banger kernel pull generic-6.12
+  banger kernel import void-kernel --from build/manual/void-kernel
+`),
+		RunE: helpNoArgs,
 	}
 	cmd.AddCommand(
 		d.newKernelListCommand(),