ESLint 10 upgrade

[svrnm]

Summary

Upgrade from ESLint 9 to ESLint 10, evaluate breaking changes, and fix any new violations.

Scope

• Review the ESLint 10 migration guide for breaking changes
• Update eslint.config.js (flat config) as needed
• Update ESLint plugins for v10 compatibility (eslint-plugin-react, eslint-plugin-import, eslint-plugin-promise, eslint-plugin-json, @tony.ganchev/eslint-plugin-header)
• Fix any new lint errors or rule changes
• Verify CI passes with the new version

Notes

Some plugins may not yet support ESLint 10 at the time of implementation — check compatibility before starting.