chore(deps): declare eslint config deps, eslint-plugin-n 18

eslint.config.js imports @eslint/js and globals but neither was declared;
both resolved transitively through eslint. Declaring them fixes a latent
break and is a prerequisite for ESLint 10, which stops providing them.

ESLint 10 itself is not taken. eslint-plugin-react 7.37.5 is the latest
release and peers at eslint "^3 || ... || ^9.7", and under 10 every rule
load throws "contextOrFilename.getFilename is not a function" because
ESLint 10 removed context.getFilename(). The frontend stays on eslint 9
until that ships; note npm already marks 9.x as no longer supported.

eslint-plugin-n goes to 18, though the flat config does not reference it
(nor eslint-plugin-import, eslint-plugin-promise or eslint-config-prettier
-- all four are unused devDependencies).

Lint output unchanged from baseline.

frontend/package.json

@@ -63,6 +63,7 @@
     "tailwind-merge": "^3.6.0"
   },
   "devDependencies": {
+    "@eslint/js": "^9.39.5",
     "@tailwindcss/postcss": "^4.3.3",
     "@types/d3-force": "^3.0.10",
     "@types/lodash": "^4.17.25",
@@ -75,11 +76,12 @@
     "eslint": "^9.39.5",
     "eslint-config-prettier": "^10.1.8",
     "eslint-plugin-import": "^2.32.0",
-    "eslint-plugin-n": "^17.24.0",
+    "eslint-plugin-n": "^18.3.0",
     "eslint-plugin-prettier": "^5.5.6",
     "eslint-plugin-promise": "^7.3.0",
     "eslint-plugin-react": "^7.37.5",
     "eslint-plugin-unused-imports": "^4.4.1",
+    "globals": "^17.12.0",
     "happy-dom": "^20.14.5",
     "husky": "^9.1.7",
     "lint-staged": "^17.5.1",