docs: 交付文档、维护指引与端到端回归

补齐 README、开发计划、维护交接与 E2E 用例，执行最终验收。

e2e/specs/widget/js-api.spec.ts

@@ -0,0 +1,25 @@
+import { test, expect } from '@e2e'
+
+test.describe('widget JS API', () => {
+  test('the host page opens and closes the chat with window.ReplyPier @widget', async ({ widget }) => {
+    await widget.embed()
+
+    await widget.api('open')
+    await expect(widget.panel).toHaveClass(/\bactive\b/)
+    await widget.expectReady()
+    expect(await widget.api('isOpen')).toBe(true)
+
+    await widget.api('close')
+    await expect(widget.panel).not.toHaveClass(/\bactive\b/)
+    expect(await widget.api('isOpen')).toBe(false)
+  })
+
+  test('a site can hide the launcher and open the chat from its own button @widget', async ({ widget }) => {
+    await widget.embed({ config: { launcher: false }, withTriggerButton: true })
+    await expect(widget.launcher).toBeHidden()
+
+    await widget.hostChatButton.click()
+    await expect(widget.panel).toHaveClass(/\bactive\b/)
+    await widget.expectReady()
+  })
+})