init: add source code from src.zip

src/commands/plan/index.ts

@@ -0,0 +1,11 @@
+import type { Command } from '../../commands.js'
+
+const plan = {
+  type: 'local-jsx',
+  name: 'plan',
+  description: 'Enable plan mode or view the current session plan',
+  argumentHint: '[open|<description>]',
+  load: () => import('./plan.js'),
+} satisfies Command
+
+export default plan