listExitNodes is resolved via the #dynamic path alias, which maps to
server/lib in the OSS build and server/private/lib in enterprise/saas.
Commit 9c18936b added a 4th siteId argument to the shared caller
(handleNewtPingRequestMessage) and to the enterprise implementation, but
not to the OSS one, so under the OSS tsconfig the call fails:
handleNewtPingRequestMessage.ts: error TS2554: Expected 1-3 arguments,
but got 4.
This breaks 'npx tsc --noEmit' for the OSS build (the CI 'Test with tsc'
step runs it after set:oss). Add siteId?: number to the OSS signature
for parity. It is unused in OSS since that build has no remote exit
nodes to label-filter; accepting it keeps the two #dynamic
implementations interface-compatible.
