chore(deps): drop unused @types/mdx devDependency from apps/docs

Nothing in apps/docs imports mdx/types or a bare *.mdx module; the
generated .source imports carry a ?collection= suffix that the *.mdx
wildcard does not match, and @types/mdx still resolves transitively via
@mdx-js/mdx for fumadocs. The docs type-check passes without the direct
edge.

Author: waleedlatif1

apps/docs/package.json

@@ -42,7 +42,6 @@
   "devDependencies": {
     "@sim/tsconfig": "workspace:*",
     "@tailwindcss/postcss": "^4.0.12",
-    "@types/mdx": "^2.0.13",
     "@types/node": "24.2.1",
     "@types/react": "^19.1.2",
     "@types/react-dom": "^19.0.4",