feat(latex): 新增 LaTeX 排版系统，从 Markdown 生成 ctexbook

- 新增 officefile/latex/ 目录，包含 main.tex、preamble.tex 及 14 个章节 + 10 个附录 tex 文件
- md→tex 转换流程：pandoc 转换 + _postprocess.py 后处理（去编号、修破折号、清标签）
- 修复 5 个 md 源文件的标题层级（H1→H2 降级，统一层级结构）
- 配置 VS Code LaTeX Workshop（xelatex + ctexbook 编译链）
- 新增 VS Code workspace 和 .gitignore（排除 LaTeX 编译产物）

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

officefile/latex/_check_nums.py

@@ -0,0 +1,23 @@
+import re, os
+
+outdir = r'e:/Project/SI/2026_DesignAI/officefile/latex/chapters'
+total = 0
+
+for fname in sorted(os.listdir(outdir)):
+    if fname == 'ch13-conclusion.tex' or not fname.endswith('.tex'):
+        continue
+    fpath = os.path.join(outdir, fname)
+    with open(fpath, 'r', encoding='utf-8') as f:
+        content = f.read()
+
+    for cmd in ['section', 'subsection', 'subsubsection']:
+        pattern = re.compile(r'\\' + cmd + r'\{(\d+\.[^}]+)\}')
+        matches = pattern.findall(content)
+        for m in matches[:3]:
+            head = m[:60]
+            print(f'  \\{cmd}{{{head}}}')
+        if len(matches) > 3:
+            print(f'  ... and {len(matches)-3} more \\{cmd} with numbers')
+        total += len(matches)
+
+print(f'\nTotal headings with numeric prefix: {total}')