ux(codex-migrate): polish preview/result output

Restructure the migrate codex CLI output:

- Split into separate Before (preview) and After (result) messages
  so each can be tuned independently. Both render through clack's
  log.message so they pick up the standard '|' gutter.
- Group items by kind (Skills, Plugins, Memory, Secrets, Archive,
  Manual review, Other) instead of one flat list. Hide config items
  from display and exclude them from the summary count.
- Drop the internal kind/action tag (e.g. 'manual/manual'), strip
  '<kind>:' id prefixes and trailing ':N' disambiguators, and use
  '•' for bullets.
- Mute parenthetical action text.
- In result mode: replace status text with emoji (✅ migrated,
  ❌ error, ⏭️ skipped, ⚠️ conflict), show '(Migrated)' on success,
  show humanized failure reasons for known codes (plugin_missing,
  marketplace_missing, etc.), say '(Skipped)' for user-deselected
  skill/plugin items but keep the real message on manual-review
  skips. Drop warnings from the result message.
- In preview mode: omit the 'Next' section and move warnings to
  the bottom. Use generic action descriptions ('Copy Codex skill
  into OpenClaw', 'Install Codex plugin into OpenClaw').
- Drop the redundant 'Codex cached plugin bundles remain
  manual-review only.' warning — covered by the source-installed
  warning above it.

extensions/codex/src/migration/plan.ts

@@ -441,9 +441,6 @@ export async function buildCodexMigrationPlan(
           "Codex app-backed plugins were planned without source app accessibility verification. Re-run with --verify-plugin-apps to force a fresh source app/list check before planning native plugin activation.",
         ]
       : []),
-    ...(source.plugins.some((plugin) => plugin.sourceKind === "cache")
-      ? ["Codex cached plugin bundles remain manual-review only."]
-      : []),
     ...(source.pluginDiscoveryError
       ? [
           `Codex app-server plugin inventory discovery failed: ${source.pluginDiscoveryError}. Cached plugin bundles, if any, are advisory only.`,