feat(macos): spike rootless Docker inside bottles

Add an opt-in docker_access path that layers rootless Docker tooling onto the selected agent image, starts the daemon only after registration, and retains the existing outer network and capability boundary. Include fail-closed bootstrap checks plus a live-Mac Compose/security acceptance test.\n\nRefs #392.

bot_bottle/backend/macos_container/bottle_plan.py

@@ -20,6 +20,7 @@ class MacosContainerBottlePlan(BottlePlan):
     # bottle is registered. See launch.py's stamp for why it lives here and not
     # only in the exec-time proxy env.
     identity_token: str = ""
+    docker_access: bool = False
 
     @property
     def container_name(self) -> str: