docs(studio): document monorepo dev server port

- Problem: @hyperframes/studio package docs showed bun run dev without the
  localhost URL contributors need after #2901 fixed contributing.mdx only.
- Fix: note that the studio dev server listens on localhost:5190 per
  packages/studio/vite.config.ts server.port.
- Verification: preflight_ship.py + read vite.config.ts; bun run format:check.

Author: santhiprakash

docs/packages/studio.mdx

@@ -45,6 +45,8 @@ bun run dev
 bun run --filter @hyperframes/studio dev
 ```
 
+The studio dev server listens on `http://localhost:5190` (see `packages/studio/vite.config.ts` `server.port`).
+
 ## Package Exports
 
 The studio has two entry points: