Rewrote structuregaps.md with function-by-function gap analysis
comparing current .NET implementation against Go reference.
Added design doc for Tier 1+2 gap closure across 4 phases:
FileStore+RAFT → JetStream Cluster → Consumer/Stream → Client/MQTT/Config.
Research documents covering implementation gaps (structuregaps.md)
and full test function mapping (testmapping.md + CSV files) between
the Go NATS server and .NET port. 857/2937 Go tests mapped (29.2%),
2080 unmatched, 2966 .NET-only tests.