Answer push_off before no_subscriptions and give every iOS browser the Home Screen copy (Feature 19)

SendTest now reads the plan_ready push preference before the stored
subscriptions, so with push off and no device subscribed the test-push
endpoint answers 409 push_off rather than 409 no_subscriptions.

Onboarding step 3's unsupported result now gives the Home Screen guidance
in any iOS browser, not only Safari. isIos in InstallHint.tsx is the one
check for iPhone, iPod and iPad; isIosSafari builds on it and InstallHint
itself stays Safari-only.

Task f89279b8-b92c-4d9f-a6c2-fd87fccda509

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/server/push.go

@@ -89,9 +89,10 @@ func deletePushSubscription(logger *slog.Logger, svc *push.Service) http.Handler
 // postTestPush answers POST /settings/notifications/test-push: it queues
 // push.TestTitle for every device that turned on push, aimed at /plan, and
 // answers 202 with the event key and how many subscriptions it goes to.
-// Delivery follows through the notification outbox. With no subscription
-// it is 409 no_subscriptions, and with push switched off for plan_ready
-// 409 push_off; neither sends anything. It never posts to Google Chat.
+// Delivery follows through the notification outbox. With push switched
+// off for plan_ready it is 409 push_off, whether or not any device has
+// turned on push; otherwise with no subscription it is 409
+// no_subscriptions. Neither sends anything. It never posts to Google Chat.
 func postTestPush(logger *slog.Logger, svc *push.Service) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		sent, err := svc.SendTest(r.Context())