docs: move execa Agent Note to implemented; update inbound links and README contracts

- proposed/testing -> implemented/testing with the lifecycle rewrite
  (Proposal->Decision in present tense, Acceptance criteria + Risks
  folded into Consequences); zh counterpart mirrored and both pairs
  re-recorded.
- the rejected NIH-audit roll-up pair now links the implemented/ path.
- loader-smoke README: captured output is bounded by execa's default
  100 MB maxBuffer, no longer unbounded.
- acp-snapshot README: harness.ts now also imports vitest (vi.waitFor),
  so the vitest-run-only constraint names both modules.
- jsonrpc keyless smoke: raise the invalid-env case's subprocess
  deadline to 25s (the 9s pick starved a cold tsx boot on slow NFS).

packages/support/loader-smoke/README.zh.md

@@ -19,5 +19,5 @@
 ## 已知限制与待完成工作
 
 - **构建 mode 需要事先构建**：配置还必须能够通过 `examples/node_modules` 向上解析每个命名包。
-- **捕获的 stdout 和 stderr 无界**：失控子进程可以消耗内存，直到 deadline 将其终止。
+- **捕获的 stdout 和 stderr 仅受 execa 默认 100 MB `maxBuffer` 约束**：失控子进程会在该上限处被终止，而不是在冒烟测试自选的预算处。
 - **超时只终止直接子进程**：故障 fixture 生成的进程树可以比冒烟测试存活更久，需要外部清理。