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>

_check_jumps.py

@@ -0,0 +1,28 @@
+import os
+
+outdir = os.path.join(os.path.dirname(__file__), 'chapters')
+for fname in sorted(os.listdir(outdir)):
+    if not fname.endswith('.tex'):
+        continue
+    fpath = os.path.join(outdir, fname)
+    with open(fpath, 'r', encoding='utf-8') as fh:
+        content = fh.read()
+    lines = content.split('\n')
+    prev_cmd = ''
+    prev_title = ''
+    for i, line in enumerate(lines):
+        s = line.strip()
+        matched = None
+        for cmd in ['\\chapter{', '\\section{', '\\subsection{', '\\subsubsection{']:
+            if s.startswith(cmd):
+                matched = cmd
+                break
+        if matched:
+            # Check for level jumps (skip of 1 or more intermediate levels)
+            levels = {'\\chapter{': 0, '\\section{': 1, '\\subsection{': 2, '\\subsubsection{': 3}
+            if prev_cmd and matched in levels and prev_cmd in levels:
+                jump = levels[matched] - levels[prev_cmd]
+                if jump > 1:
+                    title = s[len(matched):-1]
+                    print(f'{fname}:{i+1}: {prev_cmd.replace("{","")} -> {matched.replace("{","")} ({jump} levels): {title[:60]}')
+            prev_cmd = matched