[Infra] Add test, typecheck, and lint scripts and make lint run ESLint

[grantfox-oss]

Telegram (ask questions / claim the issue here first): https://t.me/+DOylgFv1jyJlNzM0

Why this matters

package.json has no test script and no typecheck script, and lint only runs prettier --check. Jest is configured but cannot be run with npm test, and ESLint (configured in eslint.config.mjs) never runs. This blocks CI from calling real commands.

Acceptance criteria

• Add test (jest) and test:watch scripts
• Add typecheck running tsc --noEmit
• Make lint run ESLint and keep a separate format:check for Prettier, or run both in lint
• Document the scripts in the README Available Scripts section

Files to touch

• package.json
• README.md

Out of scope

• Writing new tests (separate issues)

[gerani1]

i would like to work on this

[grantfox-oss]

🦊 GrantFox — @gerani1 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #12)
2. Your PR will be reviewed by the LabsCrypt maintainers

Good luck! Track your progress on GrantFox.