feat(notifications): persist stable deviceId for FCM registration

Add getOrCreateDeviceId() backed by Capacitor Preferences so one UUID
survives app restarts and token refreshes. Include deviceId in POST
/notifications/register alongside fcmToken, platform, and testMode.
Add @capacitor/preferences and lightweight DeviceId logs (no token/ID values).

package.json

@@ -148,6 +148,7 @@
     "@capacitor/core": "^6.2.0",
     "@capacitor/filesystem": "^6.0.0",
     "@capacitor/ios": "^6.2.0",
+    "@capacitor/preferences": "^6.0.4",
     "@capacitor/push-notifications": "^6.0.5",
     "@capacitor/share": "^6.0.3",
     "@capacitor/status-bar": "^6.0.2",

src/services/notifications/NotificationService.ts

@@ -15,6 +15,7 @@
 
 import { Capacitor } from "@capacitor/core";
 import { logger } from "@/utils/logger";
+import { getOrCreateDeviceId } from "./deviceId";
 import { NativeNotificationService } from "./NativeNotificationService";
 import { WebPushNotificationService } from "./WebPushNotificationService";
 
@@ -22,10 +23,12 @@ import { WebPushNotificationService } from "./WebPushNotificationService";
  * Registers an FCM device token with the app backend (native Capacitor token or web getToken).
  */
 export async function registerToken(fcmToken: string): Promise<void> {
+  const deviceId = await getOrCreateDeviceId();
   const res = await fetch("/notifications/register", {
     method: "POST",
     headers: { "Content-Type": "application/json" },
     body: JSON.stringify({
+      deviceId,
       fcmToken,
       platform: Capacitor.getPlatform(),
       testMode: true,

src/services/notifications/deviceId.ts

@@ -0,0 +1,29 @@
+import { Preferences } from "@capacitor/preferences";
+
+const DEVICE_ID_KEY = "stable_device_id";
+
+function generateDeviceId(): string {
+  return crypto.randomUUID();
+}
+
+export async function getOrCreateDeviceId(): Promise<string> {
+  const existing = await Preferences.get({ key: DEVICE_ID_KEY });
+
+  if (existing.value) {
+    // eslint-disable-next-line no-console
+    console.log("[DeviceId] Loaded existing deviceId");
+    return existing.value;
+  }
+
+  const newId = generateDeviceId();
+
+  await Preferences.set({
+    key: DEVICE_ID_KEY,
+    value: newId,
+  });
+
+  // eslint-disable-next-line no-console
+  console.log("[DeviceId] Generated new deviceId");
+
+  return newId;
+}