docs: renumber PRD 0083 -> 0081 across the reconcile chunk

Follows the base branch back to 0081. 0083 was already claimed by
feat/pinned-infra-artifacts (docs/prds/0083-packaged-infra-artifacts.md), so
the two PRDs would have collided on whichever merged second; 0081 is free.

29 references across 21 files — the "PRD 0083" prose in the backends, the
shared gateway_attach flow, the tests, and the ADR — plus the PRD filename in
the ADR's reference link, which now resolves again.

requirements.gateway.lock matches "0083" inside a sha256 hash and is
deliberately untouched.

Unit suite unchanged: same 13 pre-existing failures as main
(test_cli_start_selector, test_firecracker_cleanup).

bot_bottle/backend/macos_container/infra_launch.py

@@ -99,7 +99,7 @@ def ensure_gateway(
 
 def running_agent_containers() -> list[str]:
     """Every running agent container's name — the bottles the bring-up reconcile
-    attaches to the fresh gateway (PRD 0083). Raises `EnumerationError` if the
+    attaches to the fresh gateway (PRD 0081). Raises `EnumerationError` if the
     live set can't be determined (fail hard rather than reconcile a partial
     set)."""
     return [f"{CONTAINER_NAME_PREFIX}{agent.slug}" for agent in enumerate_active()]
@@ -108,7 +108,7 @@ def running_agent_containers() -> list[str]:
 def push_ca_to_container(name: str, ca_pem: str) -> None:
     """(Re)attach one running agent container to the current gateway: replace
     its trusted gateway CA with `ca_pem` and rebuild its trust store via
-    `container cp` + `container exec` (PRD 0083). Unconditional install — there
+    `container cp` + `container exec` (PRD 0081). Unconditional install — there
     is one gateway, so no fingerprint match is needed.
 
     Fail hard: raises `InfraLaunchError` (naming the container) on any failure —