[kedarv]

Summary

• Replace AVA with Vitest and ESLint/Prettier with Oxlint/Oxfmt.
• Add watch triggers for Jsonnet inputs, required assertions, and Vitest lint checks.
• Update CI to Node 24 and npm ci; preserve libraries and golden outputs.

Hopefully this will stem the semgrep warnings by using more modern libs?

Validation

• All 57 tests pass on Node 24 and 26; make, lint, and watch/assertion smoke checks pass.
• npm audit: zero vulnerabilities.
• npm ci succeeds with an optional macOS fsevents script-approval warning.

[linear-code]

DI-2544