docs: M2 第二波收口——报告 13~21 与契约草案入档挂导航

- 13~18 后端纵切六单报告（T2-03~08，测试 95→182）
- 14 + openapi-pets-draft.yaml 契约起草档案
- 19 契约冻结报告（v1.2.0，22 项草案修正对照）
- 20 契约一致性测试（快照机制 + 1 漂移修复）
- 21 第二波收口总表（定型语义汇总，第三波接入依据）
- mkdocs build --strict 通过

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

mkdocs.yml

@@ -43,6 +43,15 @@ nav:
           - 10 Flutter 埋点修复: development/iterations/iteration-2/10-flutter-analytics-repair.md
           - 11 后端地基报告: development/iterations/iteration-2/11-backend-foundation-report.md
           - 12 第一波收口: development/iterations/iteration-2/12-wave1-closure.md
+          - 13 宠物 CRUD 与权限框架: development/iterations/iteration-2/13-pets-crud-permission-report.md
+          - 14 契约起草说明: development/iterations/iteration-2/14-pets-contract-draft.md
+          - 15 埋点持久化队列: development/iterations/iteration-2/15-analytics-persistent-queue.md
+          - 16 体重与疫苗接口: development/iterations/iteration-2/16-weights-vaccinations-report.md
+          - 17 健康事件与提醒接口: development/iterations/iteration-2/17-events-reminders-report.md
+          - 18 档案聚合摘要: development/iterations/iteration-2/18-pet-summary-report.md
+          - 19 契约冻结报告: development/iterations/iteration-2/19-contract-freeze-report.md
+          - 20 契约一致性测试: development/iterations/iteration-2/20-contract-test-report.md
+          - 21 第二波收口: development/iterations/iteration-2/21-wave2-closure.md
   - API:
       - 契约说明: api/index.md
   - 架构: