fix: move react to peerDependencies only, fix exports for modern bundlers

react and react-dom were listed in both dependencies and peerDependencies,
causing duplicate React bundles. Now they are peer-only as intended.

Also corrects main/module/exports fields for Vite 7 compatibility and
extends React peer dependency range to include React 19.

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

Author: vepsala

package.json

@@ -30,10 +30,8 @@
     "htmlfy": "^0.7.2",
     "insane": "^2.6.2",
     "marked": "^12.0.0",
-    "react": "^17.0.0 || ^18.0.0",
     "react-colorful": "^5.6.1",
     "react-contenteditable": "^3.3.7",
-    "react-dom": "^17.0.0 || ^18.0.0",
     "zod": "^3.22.4",
     "zustand": "^4.5.1"
   },