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/visual/widget.spec.ts

@@ -0,0 +1,25 @@
+import { test, expect, customizeAgent } from '@e2e'
+
+// Screenshot baselines are generated on Linux in CI (the nightly job, or the e2e
+// workflow run by hand with "update snapshots") and committed from its artifact.
+// Never commit a baseline made on a Mac: fonts render differently.
+
+test.describe('widget appearance', () => {
+  for (const scheme of ['light', 'dark'] as const) {
+    test(`launcher and open chat, ${scheme} @visual @widget`, async ({ agent, adminApi, widget }) => {
+      // Fixed name and text, so nothing in the shot changes from run to run (the
+      // avatar is drawn from the name, too).
+      await adminApi.put(`/agent/${agent.id}`, { data: { display_name: 'Acme Support' } })
+      await customizeAgent(adminApi, agent.id, { welcome_message: 'Hi! How can we help today?' })
+      await widget.page.emulateMedia({ colorScheme: scheme })
+      await widget.embed()
+      await expect(widget.launcher).toBeVisible()
+      await expect(widget.launcher).toHaveScreenshot(`launcher-${scheme}.png`)
+
+      await widget.open()
+      await expect(widget.welcomeMessage).toBeVisible()
+      await expect(widget.agentName).toHaveText('Acme Support')
+      await expect(widget.panel).toHaveScreenshot(`chat-${scheme}.png`)
+    })
+  }
+})