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。

frontend/src/__tests__/services/knowledge.errors.spec.ts

@@ -0,0 +1,15 @@
+import { describe, it, expect, vi } from 'vitest'
+
+vi.mock('@/services/api', () => ({ default: { post: vi.fn() } }))
+
+import api from '@/services/api'
+import { knowledgeService } from '@/services/knowledge'
+
+describe('knowledgeService errors', () => {
+  it('a URL the server refuses reads as a sentence, not [object Object]', async () => {
+    vi.mocked(api.post).mockRejectedValue({
+      response: { status: 422, data: { detail: [{ loc: ['body', 'websites'], msg: 'Value error, URL must contain a valid domain with TLD' }] } },
+    })
+    await expect(knowledgeService.addUrls('org-1', ['https://localhost'])).rejects.toThrow('URL must contain a valid domain with TLD')
+  })
+})