Add package-lock.json for dependency reproducibility

[DeFiVC]

What

The chainlearn-indexer is missing a package-lock.json file, which means dependency versions are not locked and may vary between installations.

Why

Without a lock file:

• npm install may install different versions on different machines
• CI/CD builds may use different dependency versions than local development
• Bug fixes or breaking changes in dependencies can appear unexpectedly

Scope

Run npm install to generate package-lock.json and commit it.

Acceptance Criteria

• package-lock.json exists in the repository root
• npm ci installs dependencies deterministically
• No changes to package.json (dependencies unchanged)

Technical Context

• File: package.json (exists)
• Missing: package-lock.json
• Note: chainlearn-api and chainlearn-frontend already have lock files