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/mcp.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 {
+  DEFAULT_MCP_TIMEOUT,
+  MAX_MCP_TIMEOUT,
+  MIN_MCP_TIMEOUT,
+  clampMCPTimeout,
+  linesToRecord,
+  recordToLines,
+} from '@/utils/mcp'
+
+describe('clampMCPTimeout', () => {
+  it('keeps a value the API accepts', () => {
+    expect(clampMCPTimeout(120)).toBe(120)
+  })
+
+  it('pulls an over-range value down to the maximum', () => {
+    // A number input's max doesn't block submission, and the 422 that would
+    // come back carries a validation payload rather than a readable message.
+    expect(clampMCPTimeout(900)).toBe(MAX_MCP_TIMEOUT)
+  })
+
+  it('rounds a fractional value to whole seconds', () => {
+    expect(clampMCPTimeout(45.6)).toBe(46)
+    expect(clampMCPTimeout(0.4)).toBe(MIN_MCP_TIMEOUT)
+  })
+
+  it('falls back to the default when the field is empty or nonsense', () => {
+    expect(clampMCPTimeout(undefined)).toBe(DEFAULT_MCP_TIMEOUT)
+    expect(clampMCPTimeout(null)).toBe(DEFAULT_MCP_TIMEOUT)
+    expect(clampMCPTimeout(NaN)).toBe(DEFAULT_MCP_TIMEOUT)
+    expect(clampMCPTimeout(0)).toBe(DEFAULT_MCP_TIMEOUT)
+    expect(clampMCPTimeout(-5)).toBe(DEFAULT_MCP_TIMEOUT)
+  })
+})
+
+describe('KEY=value line editing', () => {
+  it('round-trips a record through the textarea form', () => {
+    const record = { AWS_REGION: 'us-east-1', AWS_ACCESS_KEY_ID: 'abc' }
+    expect(linesToRecord(recordToLines(record))).toEqual(record)
+  })
+
+  it('keeps a value containing "=" intact', () => {
+    expect(linesToRecord('Authorization=Bearer a=b')).toEqual({ Authorization: 'Bearer a=b' })
+  })
+
+  it('ignores lines without a key', () => {
+    expect(linesToRecord('novalue\n=orphan\nA=1')).toEqual({ A: '1' })
+  })
+
+  it('treats a missing record as empty', () => {
+    expect(recordToLines(undefined)).toBe('')
+  })
+})