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__/utils/text.spec.ts

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+/*
+Copyright 2024-2026 ChatterMate
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { describe, it, expect } from 'vitest'
+import { getInitials } from '@/utils/text'
+
+describe('getInitials', () => {
+  it('takes the first letter of the first two words', () => {
+    expect(getInitials('John Doe')).toBe('JD')
+    expect(getInitials('Maya Chen Rodriguez')).toBe('MC')
+    expect(getInitials('Cher')).toBe('C')
+  })
+
+  // Hyphens are part of the name, not a word boundary — splitting on them
+  // would drop the surname ("Jean-Luc Picard" → "JL" instead of "JP")
+  it('keeps hyphenated and apostrophised names intact', () => {
+    expect(getInitials('Jean-Luc Picard')).toBe('JP')
+    expect(getInitials("Anne-Marie O'Brien")).toBe('AO')
+  })
+
+  it('derives initials from an email local part', () => {
+    expect(getInitials('john.doe@example.com')).toBe('JD')
+    expect(getInitials('arun_r@example.com')).toBe('AR')
+    expect(getInitials('support@example.com')).toBe('S')
+  })
+
+  it('falls back when there is nothing to work with', () => {
+    expect(getInitials('')).toBe('?')
+    expect(getInitials(null)).toBe('?')
+    expect(getInitials(undefined)).toBe('?')
+    expect(getInitials('   ')).toBe('?')
+    expect(getInitials('', '')).toBe('')
+  })
+})