chore: switch oxlint config from .oxlintrc.json to oxlint.config.ts

Same config, just the TS form (defineConfig from 'oxlint'). Verified with
--print-config that it's actually picked up over the JSON default.

.oxlintrc.json

@@ -1,17 +0,0 @@
-{
-  "$schema": "./node_modules/oxlint/configuration_schema.json",
-  "plugins": ["typescript", "unicorn", "oxc"],
-  "categories": {
-    "correctness": "error",
-    "suspicious": "warn",
-    "pedantic": "warn"
-  },
-  "rules": {
-    "eslint/max-lines": "off",
-    "eslint/max-lines-per-function": "off"
-  },
-  "env": {
-    "builtin": true
-  },
-  "ignorePatterns": ["dist/"]
-}

oxlint.config.ts

@@ -0,0 +1,18 @@
+import { defineConfig } from 'oxlint';
+
+export default defineConfig({
+  plugins: ['typescript', 'unicorn', 'oxc'],
+  categories: {
+    correctness: 'error',
+    suspicious: 'warn',
+    pedantic: 'warn',
+  },
+  rules: {
+    'eslint/max-lines': 'off',
+    'eslint/max-lines-per-function': 'off',
+  },
+  env: {
+    builtin: true,
+  },
+  ignorePatterns: ['dist/'],
+});