Validate DFHack 53.15-r2 proto sync (no-op)

[Copilot]

What & why

DFHack 53.15-r2 required confirming vendored RPC protos were current to avoid wire-protocol drift.
This PR verifies the repo is already in sync; no file updates were needed.

• Upstream re-sync check
  • Compared local proto/*.proto against DFHack 53.15-r2 sources (library/proto + plugins/remotefortressreader/proto).
  • Result: all compared files are byte-identical (no proto deltas).
• Generated artifact consistency
  • Re-ran build pipeline (gen-proto + bundle) to confirm build/proto.json remains unchanged.
• Protocol impact
  • No wire-format or RPC schema changes in this repo for 53.15-r2.

# Representative verification pattern used
diff -q proto/RemoteFortressReader.proto /tmp/dfhack53r2/RemoteFortressReader.proto
sha256sum proto/*.proto /tmp/dfhack53r2/*.proto

How it was verified

• npm run typecheck clean
• npm run lint clean
• npm run build succeeds
• npm test passes (offline protocol test)
• If the protocol changed: re-ran npm run gen-proto and committed build/proto.json

Notes

No repository changes were required; this is an explicit no-op closure for the version bump validation.