Add initial project files

packages/hooks/src/useBodyClass/Readme.md

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+# useBodyClass
+
+Adds one or more CSS classes to `document.body` while the component is mounted, and removes them on unmount.
+
+## Signature
+
+```ts
+function useBodyClass(className: string): void;
+```
+
+| Parameter   | Type     | Description                                             |
+| ----------- | -------- | ------------------------------------------------------- |
+| `className` | `string` | Space-separated class name(s) to add to `document.body` |
+
+## Usage
+
+```tsx
+export function ModalLayout({ children }: { children: React.ReactNode }) {
+  useBodyClass('overflow-hidden bg-overlay');
+
+  return <div>{children}</div>;
+}
+```
+
+While `ModalLayout` is mounted, `document.body` will have the classes `overflow-hidden` and `bg-overlay`. Both are removed automatically when the component unmounts.
+
+## Notes
+
+- Accepts a space-separated string — multiple classes are handled individually so partial removal is safe.
+- Re-applies classes if the `className` prop changes.
+- Client-only (`'use client'`). Does not run during SSR.