docs: M2 第一波收口——报告 09/10/11 入档挂导航

- 09 契约补录 events（关闭 D-1/放行条件②，另含实现与旧规范 5 处出入记录）
- 10 Flutter 埋点修复（接线+三偏差+SessionTracker+page_viewed，34→51 测试，12/12 验收）
- 11 后端地基（V3/V4 迁移 8 表+种子、4 条跨 schema FK 剥离、patbond-pet 骨架、ADR-013 执行，82→95 测试）
- mkdocs build --strict 通过

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

mkdocs.yml

@@ -39,6 +39,9 @@ nav:
           - 06 埋点规划: development/iterations/iteration-2/06-experiment-tracking-plan.md
           - 07 证据基线审计: development/iterations/iteration-2/07-evidence-baseline-audit.md
           - 08 Git 工作流规划: development/iterations/iteration-2/08-git-workflow-plan.md
+          - 09 契约补录 events: development/iterations/iteration-2/09-events-contract-backfill.md
+          - 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
   - API:
       - 契约说明: api/index.md
   - 架构: