Consider JS/MJS/CJS support in TypeScript and ESLint configs

[gtbuchanan]

Summary

The shared tsconfig and eslint-config packages currently only target TypeScript files. Consider extending support to JavaScript files (.js, .mjs, .cjs) and ensuring .mts/.cts coverage.

Context

The eslint-config strictTypeChecked preset and projectService require linted files to be part of a TypeScript project. JavaScript files outside the tsconfig include cause was not found by the project service errors.

Most plugin configs in eslint-config use **/*.ts without .mts/.cts — only node.ts includes all three. A shared tsFiles pattern would ensure consistency.

Areas to evaluate

• tsconfig: Add allowJs: true and include JS file patterns in generated tsconfigs
• eslint-config: Define a shared tsFiles glob (.ts, .mts, .cts) used by all plugin configs, and extend to JS when ready
• disableTypeChecked: Currently covers JSON/YAML — may need to cover JS files if allowJs isn't enabled, or use allowDefaultProject as a fallback
• vitest: Test file patterns (**/test/**/*.ts, **/e2e/**/*.ts) should also cover .mts/.cts
• entryPoints: Default patterns (**/bin/**/*.ts, **/scripts/**/*.ts) should also cover .mts/.cts

Motivation

Consumer repos may have JS files (config files, scripts, legacy code) that should be linted by the shared config. Even without JS support, .mts/.cts files are currently missed by most plugin configs.