Add initial project files

packages/hooks/src/useViewport/Readme.md

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+# useViewport
+
+Returns the current viewport dimensions `[height, width]` and updates them on window resize.
+
+## Signature
+
+```ts
+function useViewport(): [number, number];
+```
+
+Returns a tuple `[height, width]` in pixels.
+
+## Usage
+
+```tsx
+function ResponsiveCanvas() {
+  const [height, width] = useViewport();
+
+  return <canvas height={height} width={width} />;
+}
+```
+
+```tsx
+// Destructure with descriptive names
+const [viewportHeight, viewportWidth] = useViewport();
+```
+
+## Notes
+
+- Reads `window.innerHeight` and `window.innerWidth` — includes the scrollbar area.
+- Initialized from the current window size, so there is no flash to `[0, 0]`.
+- Client-only (`'use client'`). Will throw during SSR if accessed before mount — pair with `useMounted` if SSR is a concern.