Addresses argus's review of #1718: the HIVE_FORGE_URL / HIVE_MATRIX_URL
conditionals still keyed off the now-deprecated `network.enable`, so
setting it to `false` would point agents at host loopback (unreachable
from their private netns) even though isolation stays on — contradicting
the "deprecated and ignored" warning. Guard on the top-level
`hyperhive.enable` instead, so `network.enable` truly has no effect
anywhere and the loopback branch only covers a hyperhive-disabled host.
Eval-proven: with `network.enable = false`, HIVE_FORGE_URL now resolves
to the gateway vhost (`http://forge.<domain>`), and the deprecation
warning still fires.
61db5afc22