refactor(ui): extract stdio plugin package

Move the readline front door from stdio-agent into @deepseek-ai/dsh-stdio, keeping the loader shape and the stdio coverage with the new package.

packages/ui/stdio/tests/plugin-shape.spec.ts

@@ -0,0 +1,19 @@
+import { describe, expect, it } from 'vitest'
+import Loader from '@cordisjs/plugin-loader'
+import * as stdio from '../src/index.ts'
+
+/** Real Loader export-path guard for the namespace stdio plugin. */
+describe('dsh-stdio plugin export shape', () => {
+  it('preserves name, inject, Config, and apply through Loader unwrapping', () => {
+    expect('default' in stdio).toBe(false)
+    expect(typeof stdio.apply).toBe('function')
+
+    const loader = Object.create(Loader.prototype) as Loader
+    const unwrapped = loader.unwrapExports(stdio) as Record<string, unknown>
+    expect(unwrapped).toBe(stdio)
+    expect(unwrapped.name).toBe('ui-stdio')
+    expect(unwrapped.inject).toEqual(['agents', 'userInteraction'])
+    expect(unwrapped.Config).toBeDefined()
+    expect(typeof unwrapped.apply).toBe('function')
+  })
+})