fix: Constrain root eslint to v8 to match core dependency

Add eslint@^8 to root package.json devDependencies to ensure npm
uses eslint 8.x instead of 9.x. The core package requires eslint@^8,
but @typescript-eslint/parser@8.x allows either eslint 8 or 9. Without
an explicit constraint, npm install was choosing eslint 9, causing the
lock file to be out of sync with core's requirements and breaking CI.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

package.json

@@ -16,6 +16,7 @@
   "devDependencies": {
     "@typescript-eslint/parser": "^8.40.0",
     "concurrently": "^9.1.2",
+    "eslint": "^8",
     "eslint-plugin-import": "^2.29.1",
     "husky": "^9.1.7",
     "lint-staged": "^15.5.2",