build(deps): pin @eslint/js explicitly so ESLint 10 can install

`eslint.config.mjs` imports from `@eslint/js`, which under ESLint 9 was
satisfied transitively. ESLint 10 dropped the transitive availability,
so a fresh `npm ci` fails to resolve the import (verified on the
Dependabot ESLint 10 PR: `ERR_MODULE_NOT_FOUND: Cannot find package
'@eslint/js'`).

Promote `@eslint/js` to an explicit devDependency. The range is set
to `^9.39.4` (matches what ESLint 9 currently resolves transitively)
so this commit is a no-op on the current toolchain — but it unblocks
the upcoming ESLint 10 bump without further config changes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: tkirda-bison

package-lock.json

@@ -48,6 +48,7 @@
     "jquery": ">=3.0"
   },
   "devDependencies": {
+    "@eslint/js": "^9.39.4",
     "@types/jquery": "^3.5.32",
     "esbuild": "^0.28.0",
     "eslint": "^9.30.1",