fix(gateway): warn on placement session evidence pipeline failure (#1…

fix(gateway): warn on placement session evidence pipeline failure (#124635)

The worker placement session evidence resolver swallowed every pipeline
failure into a bare catch that returned "unknown" for all placements.
Fail-open is correct for retirement safety, but the silent catch hid a
broken evidence pipeline (bad config, store corruption) behind indefinite
placement retention with no operator-visible signal. Record the fact at
the boundary that owns it: warn with the error before returning unknown.

Also collapse the byte-identical publish branches in
acquirePreparedModelRuntimeLeaseFromOwners: staleDynamicOwner and
missing-owner both published the exact same snapshot call; one branch
now owns publication with the invariant comment preserved.