feat: add DocumentEditor with dirty tracking and save

frontend/src/components/DocumentEditor.tsx

@@ -0,0 +1,71 @@
+import { useEffect, useState } from 'react';
+import Editor from '@monaco-editor/react';
+import { getDocument, saveDocument } from '../api/client';
+
+interface DocumentEditorProps {
+  documentKey: string;
+}
+
+export default function DocumentEditor({ documentKey }: DocumentEditorProps) {
+  const [content, setContent] = useState('');
+  const [originalContent, setOriginalContent] = useState('');
+  const [contentType, setContentType] = useState('text/markdown');
+  const [loading, setLoading] = useState(true);
+  const [saving, setSaving] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+
+  useEffect(() => {
+    setLoading(true);
+    setError(null);
+    getDocument(documentKey)
+      .then((doc) => {
+        setContent(doc.content);
+        setOriginalContent(doc.content);
+        setContentType(doc.contentType);
+        setLoading(false);
+      })
+      .catch(() => {
+        setError('无法加载文档');
+        setLoading(false);
+      });
+  }, [documentKey]);
+
+  const isDirty = content !== originalContent;
+
+  function handleChange(value: string | undefined) {
+    setContent(value ?? '');
+  }
+
+  function handleSave() {
+    setSaving(true);
+    saveDocument(documentKey, content, contentType)
+      .then(() => {
+        setOriginalContent(content);
+        setSaving(false);
+      })
+      .catch(() => {
+        setError('保存失败');
+        setSaving(false);
+      });
+  }
+
+  if (loading) {
+    return <div data-testid="document-editor-loading">加载中…</div>;
+  }
+
+  if (error) {
+    return <div data-testid="document-editor-error">{error}</div>;
+  }
+
+  return (
+    <div data-testid="document-editor">
+      <div className="doc-header">
+        <span data-testid="save-status">{isDirty ? '未保存' : '已归档'}</span>
+        <button onClick={handleSave} disabled={!isDirty || saving}>
+          {saving ? '保存中…' : '保存'}
+        </button>
+      </div>
+      <Editor value={content} onChange={handleChange} language={contentType === 'text/markdown' ? 'markdown' : 'html'} />
+    </div>
+  );
+}

frontend/tests/components/DocumentEditor.test.tsx

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+import { render, screen } from '@testing-library/react';
+import { vi, test, expect, beforeEach } from 'vitest';
+import DocumentEditor from '../../src/components/DocumentEditor';
+import { getDocument, saveDocument } from '../../src/api/client';
+
+vi.mock('../../src/api/client');
+
+vi.mock('@monaco-editor/react', () => ({
+  default: ({ value, onChange }: { value: string; onChange: (value: string | undefined) => void }) => (
+    <textarea
+      data-testid="monaco-editor-mock"
+      value={value}
+      onChange={(e) => onChange(e.target.value)}
+    />
+  ),
+}));
+
+beforeEach(() => {
+  vi.mocked(getDocument).mockReset();
+  vi.mocked(saveDocument).mockReset();
+});
+
+test('shows a loading state, then loads and displays document content', async () => {
+  vi.mocked(getDocument).mockResolvedValue({
+    key: '产品文档/架构设计.md',
+    content: '# 架构设计',
+    contentType: 'text/markdown',
+  });
+
+  render(<DocumentEditor documentKey="产品文档/架构设计.md" />);
+
+  expect(screen.getByTestId('document-editor-loading')).toBeInTheDocument();
+
+  const textarea = await screen.findByTestId('monaco-editor-mock');
+  expect(textarea).toHaveValue('# 架构设计');
+  expect(getDocument).toHaveBeenCalledWith('产品文档/架构设计.md');
+  expect(screen.getByTestId('save-status')).toHaveTextContent('已归档');
+});
+
+import userEvent from '@testing-library/user-event';
+import { waitFor } from '@testing-library/react';
+
+test('typing marks the document dirty and saving clears the dirty state', async () => {
+  vi.mocked(getDocument).mockResolvedValue({
+    key: '产品文档/架构设计.md',
+    content: '# 架构设计',
+    contentType: 'text/markdown',
+  });
+  vi.mocked(saveDocument).mockResolvedValue({
+    key: '产品文档/架构设计.md',
+    updatedAt: '2026-08-01T10:05:00Z',
+  });
+  const user = userEvent.setup();
+
+  render(<DocumentEditor documentKey="产品文档/架构设计.md" />);
+
+  const textarea = await screen.findByTestId('monaco-editor-mock');
+  await user.clear(textarea);
+  await user.type(textarea, '# 新内容');
+
+  expect(screen.getByTestId('save-status')).toHaveTextContent('未保存');
+
+  const saveButton = screen.getByRole('button', { name: '保存' });
+  await user.click(saveButton);
+
+  await waitFor(() => {
+    expect(saveDocument).toHaveBeenCalledWith('产品文档/架构设计.md', '# 新内容', 'text/markdown');
+  });
+  await waitFor(() => {
+    expect(screen.getByTestId('save-status')).toHaveTextContent('已归档');
+  });
+});