build: lint JavaScript and JSON from one eslint config

[BrandonLWhite]

Summary

Follow-up to #28. super-linter shares one config variable (JAVASCRIPT_ES_LINTER_RULES) across its JAVASCRIPT_ES, JSON, JSONC and VUE linters, so pointing it at this repo's eslint.config.mjs would have silently stopped JSON linting — our config had no JSON language support, and an invalid .json file came back File ignored because no matching configuration was supplied with exit 0. #28 worked around that by disabling VALIDATE_JAVASCRIPT_ES, which left super-linter linting JSON with its own bundled config.

This makes one config cover both, so npm run lint and super-linter enforce the same rules over the same files.

Actions

• Added @eslint/json and JSON + JSONC language blocks to eslint.config.mjs.
• Scoped the JavaScript configs to js/mjs/cjs. js.configs.recommended, eslint-plugin-jest and eslint-plugin-prettier declare no files of their own, so their rules would otherwise be applied to JSON files.
• Added .github/linters/eslint.config.mjs, re-exporting the root config, because JAVASCRIPT_ES_CONFIG_FILE resolves under LINTER_RULES_PATH (.github/linters) and not the repo root.
• Removed VALIDATE_JAVASCRIPT_ES: false from linter.yml.
• Turned off json/no-empty-keys for package-lock.json only — npm's packages map uses "" for the root project. The other three JSON rules still apply to it, rather than skipping the file.

Verification

• JS rule parity: eslint --print-config src/main.js is byte-identical in effect before and after — 82 active rules, none lost, none added.
• Coverage went up: 15 files linted → 17, now including package.json and package-lock.json.
• It actually lints (not a silent no-op): with eslint 9.39.4, the version inside the super-linter container, invoked as super-linter does (eslint -c .github/linters/eslint.config.mjs <abs path>):
  • injected duplicate JSON key → json/no-duplicate-keys, exit 1
  • injected duplicate JS binding → parse error, exit 1
  • unmodified repo files → exit 0, no warnings
• npm run lint, npm run format:check, npm run ci-test (4 suites / 10 tests) all clean; npm run package leaves dist/ unchanged.
• zizmor (v1.25.2, matching the container) still reports no findings.

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