Two argus review fixups:
1. Move isolateContainers assertion to an unconditional `lib.mkIf
cfg.isolateContainers` arm. The prior placement inside
`mkIf (enable && isolateContainers)` was dead code — the assertion
could never fire because both flags were already true by the time the
block activated. Now `isolateContainers=true; enable=false;` raises
a NixOS assertion error at eval time.
2. Add comment on HIVE_NETWORK_SUBNET noting it carries the host-side
bridge IP (e.g. "10.42.0.1/24"), not the canonical network address
("10.42.0.0/24"). Rust consumer must normalize via bitwise AND before
subnet membership checks or address arithmetic.
c1b40ef819