CI's nix flake check ran in hive-ci's OWN in-container nix-daemon, which
offloads to the pc2 remote builder and HARD-FAILS when pc2 is
unreachable (Connection-reset) — reddening every PR's queue hive-wide.
The host daemon builds fine in the same situation (buildMachines +
max-jobs>=1 + fallback → local build when pc2 is down), and the agent
containers already route through it.
Give hive-ci the same wiring: bind-mount the host nix-daemon socket dir
into the container, set NIX_REMOTE=daemon, and disable the container's
own nix-daemon service + socket. Now CI builds through the host daemon —
pc2 offload when it's up, graceful local fallback when it's down. Drops
the now-moot in-container wait-nix-daemon precond. Needs an operator
rebuild to apply.