ui/hooks: add clickOutside hook

pkgs/clan-app/ui/src/hooks/useClickOutside.tsx

@@ -0,0 +1,15 @@
+import { onCleanup } from "solid-js";
+
+export function useClickOutside(
+  el: () => HTMLElement | undefined,
+  handler: (e: MouseEvent) => void,
+) {
+  const listener = (e: MouseEvent) => {
+    const element = el();
+    if (element && !element.contains(e.target as Node)) {
+      handler(e);
+    }
+  };
+  document.addEventListener("mousedown", listener);
+  onCleanup(() => document.removeEventListener("mousedown", listener));
+}