Fix openapi package exports: use bun/types/import pattern

The exports map pointed all conditions at source ./index.ts, which
breaks Node after build — index.ts imports ./specParser.js but only
.ts source files exist. Node needs the built dist/ files.

Use the same pattern as other packages: bun→source for dev,
types/import→dist for Node. Drop the unused publishConfig.exports
since this package is private.

Fixes: bin.js spec exited with code 1: ERR_MODULE_NOT_FOUND
Committed-By-Agent: claude

Author: tonyxiao

packages/openapi/package.json

@@ -5,17 +5,9 @@
   "type": "module",
   "exports": {
     ".": {
-      "types": "./index.ts",
-      "import": "./index.ts",
-      "default": "./index.ts"
-    }
-  },
-  "publishConfig": {
-    "exports": {
-      ".": {
-        "types": "./dist/index.d.ts",
-        "import": "./dist/index.js"
-      }
+      "bun": "./index.ts",
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.js"
     }
   },
   "scripts": {