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.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write
-README.md: 8e53550608037a3c9a272db825933b7224ab24db
-README.zh.md: 5310429ab59cf3cd04ac024746f5ed557e003637
+README.md: 73610ce50ebac4c6fc7bb9135f7b41b347c60685
+README.zh.md: 17f8481220136e8edf9fccd23fabfca5ccf41dfc