The BTCPayServer hub entry was using `cfg.services.bitcoin` as its
`enabled` flag, which is `true` in node mode. This caused the Hub UI
to show BTCPayServer as enabled even though the underlying NixOS service
is correctly gated on `cfg.web.btcpayserver` (which defaults to `false`
for the node role via role-logic.nix).
Change the enabled field to `cfg.web.btcpayserver` so the Hub UI
accurately reflects the service state and BTCPayServer is disabled by
default on a fresh node-only install.
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