feat(core): modems run — the pair in the project, and a modem of another project hands its frames on (K0–K2)

Measured first: tools/java-oracle's ModemRun joins two networks by a pair
of Java modems over TCP on localhost. The modem has no card and adds no
delay of its own — a frame takes the cables on both sides, nothing more.

The core pairs the two enabled modems on a port (Swift's inProject, with
its conditions and cycle suppression) on Java's timing: no 20 ms. The
modem example of FILIUS now pings through instead of failing the core.
A modem of another project (relay) gives its frames to whoever runs the
engine and puts on its cable what comes back, with this engine's frame
and packet numbers; a frame dies after MAXIMUM_RELAY_HOPS trips.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/fls/src/projectSnapshot.ts

@@ -59,6 +59,7 @@ export function projectSnapshot(project: ImportedProject): TopologySnapshot {
     firewallConfigurationsByNodeId: project.firewallConfigurationsByNodeId,
     portForwardingRowsByNodeId: project.portForwardingRowsByNodeId,
     switchConfigurationsByNodeId: project.switchConfigurations,
+    remoteLinkConfigurationsByNodeId: project.remoteLinkConfigurations,
     ipForwardingByNodeId: project.ipForwardingByNodeId,
     echoServersByNodeId: echoServers,
     simpleClientsByNodeId: project.simpleClientConfigurations,