Re-enable ESLint in vite-plugin-checker when ESLint v10 is supported

[jasontaylordev]

Summary

ESLint was removed from vite-plugin-checker configuration in #2832 because vite-plugin-checker doesn't support ESLint v10.

Background

When upgrading to ESLint v10, vite-plugin-checker fails with:

Error: Invalid Options:
- Unknown options: extensions, ignorePath, reportUnusedDisableDirectives, resolvePluginsRelativeTo, rulePaths, useEslintrc

These options were deprecated/removed in ESLint v10's new options API.

Upstream tracking

• vite-plugin-checker issue Support ESLint v10.x fi3ework/vite-plugin-checker#647

Desired outcome

Once vite-plugin-checker releases a version with full ESLint v10 support, re-enable the ESLint checker in vite.config.ts:

checker({
  overlay: { initialIsOpen: "error" },
  vueTsc: { tsconfigPath: "tsconfig.app.json" },
  eslint: { lintCommand: "eslint ." }
})

Current workaround

Developers should use IDE ESLint integration (see docs/frontend/frontend-ide.md) or run npm run lint manually. CI still runs lint checks.