feat(docs): Markdown 展示路由源码位置 (issue #5)

[yourtion]

关联 issue

Closes #5

改动内容

sourceFile（含 relative/absolute，由 getCallerSourceLine 在路由注册时解析 Error.stack 采集）此前已在 API 构造时记录，但未纳入 DOC_FIELD，文档生成器拿不到。

• 将 sourceFile 加入 DOC_FIELD
• Markdown 在「请求地址」行下方输出 源码位置：<relative>
• 无 sourceFile 时不输出该行，行为不变

测试

• 新增 2 个回归测试（有/无 sourceFile）
• 全量 npm run test:lib：317 → 319 全绿
• tsc --noEmit 通过

版本

bump 3.2.1 → 3.2.4，已登记 MIGRATION

合并顺序提示

本系列共 4 个 PR，请按版本号顺序合并（3.2.2 → 3.2.3 → 3.2.4 → 3.2.5）。
⚠️ 合并时 MIGRATION.md 与 package.json 可能冲突，需 rebase 解冲突。

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.56%. Comparing base (ffe0ffa) to head (a311cf3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #196      +/-   ##
==========================================
+ Coverage   92.54%   92.56%   +0.01%     
==========================================
  Files          28       28              
  Lines        2939     2944       +5     
  Branches      770      772       +2     
==========================================
+ Hits         2720     2725       +5     
  Misses        217      217              
  Partials        2        2              

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