chore: switch lint scripts from removed next lint to eslint

Next 16 removed the `next lint` subcommand, so `npm run lint` failed with
"Invalid project directory provided, no such directory: .../lint". Point the
lint and lint:fix scripts at ESLint directly, using the existing flat config
(eslint.config.mjs).

package.json

@@ -25,8 +25,8 @@
     "dev": "next dev --turbopack",
     "build": "next build --turbopack",
     "start": "next start",
-    "lint": "next lint",
-    "lint:fix": "next lint --fix",
+    "lint": "eslint .",
+    "lint:fix": "eslint . --fix",
     "test:translations": "vitest run --no-isolate lib/__tests__/translations.test.ts",
     "prepare": "husky",
     "typecheck": "tsc --noEmit"