Address review feedback: Use <Option> components, remove `overwrite`, re-export types from @remotion/renderer

- Convert inline option descriptions to <Options> components in render-media-on-vercel.mdx
- Remove `overwrite` option from public API (sandboxes are ephemeral)
- Add @remotion/renderer as dependency and re-export types instead of redefining them
- Update homepage URL to /docs/vercel/api