Push notifications: period soon/late reminders, test button

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

static/sw.js

@@ -0,0 +1,29 @@
+// Service worker: only shows push notifications. It deliberately caches
+// nothing, so the app always loads fresh from the server.
+self.addEventListener("install", () => self.skipWaiting());
+self.addEventListener("activate", event => event.waitUntil(self.clients.claim()));
+
+self.addEventListener("push", event => {
+  let message = { title: "Flowtrack", body: "" };
+  try {
+    message = { ...message, ...event.data.json() };
+  } catch {
+    // An empty or unreadable push still has to show something on iOS.
+  }
+  event.waitUntil(self.registration.showNotification(message.title, {
+    body: message.body,
+    icon: "/icon-192.png",
+    badge: "/icon-192.png",
+    tag: message.tag,
+    data: { url: message.url || "/" }
+  }));
+});
+
+self.addEventListener("notificationclick", event => {
+  event.notification.close();
+  event.waitUntil((async () => {
+    const windows = await self.clients.matchAll({ type: "window", includeUncontrolled: true });
+    if (windows.length) return windows[0].focus();
+    return self.clients.openWindow(event.notification.data.url);
+  })());
+});