fix: webpush for iOS

lib/push.ts

@@ -22,6 +22,37 @@ export function pushSupported(): boolean {
   );
 }
 
+/** iPhone/iPad/iPod (incl. iPadOS, which reports as "Macintosh" + touch). */
+export function isIOS(): boolean {
+  if (typeof navigator === "undefined") return false;
+  const ua = navigator.userAgent;
+  return (
+    /iPad|iPhone|iPod/.test(ua) ||
+    (navigator.maxTouchPoints > 1 && /Macintosh/.test(ua))
+  );
+}
+
+/** Running as an installed (Home Screen) app, not a browser tab. */
+export function isStandalone(): boolean {
+  if (typeof window === "undefined") return false;
+  return (
+    // iOS Safari's non-standard flag…
+    (navigator as Navigator & { standalone?: boolean }).standalone === true ||
+    // …and the standard display-mode for everyone else.
+    window.matchMedia("(display-mode: standalone)").matches
+  );
+}
+
+/**
+ * iOS only allows Web Push when the site has been added to the Home Screen
+ * (iOS 16.4+). In a plain Safari tab the push APIs don't exist, so this is
+ * the case where we should guide the user to "Add to Home Screen" rather
+ * than show a dead "unsupported".
+ */
+export function needsIOSInstall(): boolean {
+  return isIOS() && !isStandalone() && !pushSupported();
+}
+
 /** The browser's current notification permission, or "unsupported". */
 export function pushPermission(): NotificationPermission | "unsupported" {
   if (!pushSupported()) return "unsupported";