fix: use conditional exports for proper CJS/ESM type resolution

Fixes FalseCJS error from @arethetypeswrong/cli.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: brmn

package.json

@@ -7,9 +7,14 @@
   "types": "dist/index.d.ts",
   "exports": {
     ".": {
-      "types": "./dist/index.d.ts",
-      "import": "./dist/index.mjs",
-      "require": "./dist/index.js"
+      "import": {
+        "types": "./dist/index.d.mts",
+        "default": "./dist/index.mjs"
+      },
+      "require": {
+        "types": "./dist/index.d.ts",
+        "default": "./dist/index.js"
+      }
     },
     "./package.json": "./package.json"
   },