closes#788. drops the per-role HIVE_LABEL fallback const ('hive-ag3nt'
on AgentSurface, 'hm1nd' on ManagerSurface) and replaces both with a
single literal 'hive' at the env-var unwrap site. real deploys set
HIVE_LABEL unconditionally via the meta-flake envelope; the fallback
is unreachable in production and there's no semantic reason for it to
differ per role.
nix-side standalone-eval fallback (HIVE_LABEL = 'hm1nd' in the
manager systemd unit) stays — that's wired so 'nixos-rebuild against
nixosConfigurations.manager' produces a sensibly-labelled container
even without the meta-flake wrapper.
Surface trait now: FLAVOR + FORGE_IS_MANAGER + 7 async wire methods.
next steps per #778 roadmap: #691 → #786 → #789.
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