[codex] Build Jussi graph artifacts

[nicholaspai]

What changed

• added scripts/buildJussiGraph.ts plus a yarn build-jussi-graph entrypoint for generating a Jussi graph bundle from current repo state
• added src/jussi/buildGraph.ts, checked-in sample graph artifacts, and src/jussi/README.md documenting how to build and inspect the bundle locally
• added focused graph-builder tests covering node extraction, bridge candidate discovery, latency handling, OFT quoting, and envelope serialization

Why

This makes the Jussi graph build flow reviewable as its own unit on top of current master, instead of coupling it to pending rebalancer route and Binance adapter changes.

Impact

Operators can generate the Jussi graph JSON, rate-limit buckets, and example prices_by_asset payload from the relayer inventory/rebalancer configuration already in this repo.

This PR no longer changes production src/rebalancer behavior; it only adds graph-builder tooling, fixtures, and tests.

Validation

• yarn build
• yarn test test/JussiGraph.buildGraph.ts