feat(docs): Swagger/Postman 展示返回结果 response schema (issue #6)

[yourtion]

关联 issue

Closes #6

改动内容

• Swagger：responses.200 输出标准 schema（type/properties/required），此前写死 { description: "请求成功" } 完全忽略 responseSchema
• Postman：每个 item 输出 response 示例（按 schema 字段名+类型生成占位 body）
• 两者都复用 extractDocFields，与参数提取保持一致
• 未声明 response schema 时保持原有占位行为不变（向后兼容）

测试

• 新增 5 个回归测试（swagger 3 + postman 2）
• 全量 npm run test:lib：317 → 322 全绿
• tsc --noEmit 通过

版本

bump 3.2.1 → 3.2.2，已登记 MIGRATION

合并顺序提示

本系列共 4 个 PR（#6 / #27 / #5 / #4），各基于 main 独立 bump 版本（3.2.2 / 3.2.3 / 3.2.4 / 3.2.5）。请按版本号顺序合并，从本 PR（3.2.2）开始。

[codecov]

Codecov Report

❌ Patch coverage is 96.61017% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.54%. Comparing base (1a5d8cc) to head (c98cfa9).

Files with missing lines	Patch %	Lines
src/lib/plugin/generate_postman/index.ts	93.93%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #194      +/-   ##
==========================================
+ Coverage   92.47%   92.54%   +0.07%     
==========================================
  Files          28       28              
  Lines        2883     2939      +56     
  Branches      747      770      +23     
==========================================
+ Hits         2666     2720      +54     
- Misses        215      217       +2     
  Partials        2        2              

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