fix(push): reinstalled app replaces its old subscription; devices listed and removable

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

frontend/src/lib/push.ts

@@ -64,7 +64,40 @@ export async function enablePush(): Promise<void> {
       throw new Error('Der Browser hat die Anmeldung beim Push-Dienst abgelehnt (Berechtigung blockiert oder Push-Dienst nicht erreichbar)');
     }
   }
-  await api.subscribePush(sub.toJSON(), deviceName());
+  // The address this browser registered before is dead once it has a new one (e.g. after reinstalling
+  // the app): the server drops it right away instead of counting it as another device
+  const previous = readStoredEndpoint();
+  await api.subscribePush(sub.toJSON(), deviceName(), previous && previous !== sub.endpoint ? previous : undefined);
+  storeEndpoint(sub.endpoint);
+}
+
+const ENDPOINT_KEY = 'mindsift_push_endpoint';
+
+function readStoredEndpoint(): string | null {
+  try {
+    return localStorage.getItem(ENDPOINT_KEY);
+  } catch {
+    return null;
+  }
+}
+
+function storeEndpoint(endpoint: string | null): void {
+  try {
+    if (endpoint) localStorage.setItem(ENDPOINT_KEY, endpoint);
+    else localStorage.removeItem(ENDPOINT_KEY);
+  } catch {
+    // storage blocked: the dead device is removed on the next push instead
+  }
+}
+
+/** Removes one of the own devices (e.g. an old installation) on the server. */
+export async function removePushDevice(endpoint: string): Promise<void> {
+  const here = await currentPushSubscription();
+  if (here?.endpoint === endpoint) {
+    await disablePush();
+    return;
+  }
+  await api.unsubscribePush(endpoint);
 }
 
 export async function disablePush(): Promise<void> {
@@ -73,4 +106,5 @@ export async function disablePush(): Promise<void> {
   const endpoint = sub.endpoint;
   await sub.unsubscribe().catch(() => false);
   await api.unsubscribePush(endpoint).catch(() => {});
+  storeEndpoint(null);
 }