Verify EulerChains.json is in sync with addresses

[kasperpawlowski]

Summary

• Add a PR-gating GitHub Actions workflow that re-runs node chains.js and fails if the committed EulerChains.json differs from what the generator produces against the current addresses/ and config/addresses/ trees.
• Motivation: EulerChains.json is a generated artifact, but nothing stops it from drifting from its source of truth. A contributor can hand-edit the manifest, or update an addresses file and forget to re-run the generator. Both are silent today.

Changes

• New workflow .github/workflows/verify-chains-manifest.yml runs on pull_request and push to master, scoped via paths to changes that could affect the output: chains.js, EulerChains.json, addresses/**, config/addresses/**. Also exposes workflow_dispatch for manual re-runs.
• The job checks out the tree, sets up Node 20, runs node chains.js, and then runs git diff --quiet -- EulerChains.json. On drift, emits a GitHub ::error:: annotation pointing contributors to run node chains.js locally, then prints the diff for context and exits 1.
• No npm install step — chains.js uses only Node built-ins (fs), so there are no dependencies to cache or pin.
• Verified on the current tree: node chains.js produces a byte-identical EulerChains.json right now, so the check starts green.

Required follow-up (repo admin)

• To actually block merges, add verify-chains-manifest as a required status check in the branch protection rule for master. Without that, the workflow will report status but will not prevent merging.

Test plan

• Open a PR that edits an addresses file (e.g. addresses/1/LensAddresses.json) without re-running chains.js — workflow must fail with the "out of sync" error and show the diff in the job log.
• On the same PR, run node chains.js locally, commit the updated EulerChains.json, push — workflow must pass.
• Open a PR that hand-edits EulerChains.json only — workflow must fail (the regenerated file will overwrite the hand-edit and the diff will surface).
• Open a PR that does not touch any of the scoped paths (e.g. README only) — workflow is correctly skipped (path filter), and skipped required checks are treated as passed by branch protection.
• Trigger the workflow manually via workflow_dispatch on master — must report "EulerChains.json matches the output of chains.js."