Fix unchecked error returns on bf.Seek(), db.Exec(), QueryRow().Scan(),
pkt.Build(), logger.Sync(), and binary.Write() calls. The linter now
passes with 0 errors, build compiles, and all tests pass with -race.
Resolve conflict in handlers_stage.go: keep lock-free packet
building pattern (copy session list, release lock, then build)
over upstream's in-lock QueueSendMHF approach.
Fix test compilation: remove objectIDs field references after
upstream removed it from Server struct.
Resync vendor directory with updated go.mod dependencies.
