feat(server): name the event in a push and offer a booking as a Google Wallet pass

The push payload carries the event it reports, so the Android app can file a
notification under a channel of its own (chat, trip updates, invitations).
A browser and the iOS extension ignore the field.

GET /api/trips/:tripId/reservations/:id/wallet-pass/google sends the same
request the Apple Wallet signer takes to the TREK services' Google route and
answers with the signed save-to-wallet link the Android app opens. Off with the
other TREK services, and a clear 404 while liketrek has no Wallet issuer yet.

shared/src/notification/notification.schema.spec.ts

@@ -199,5 +199,7 @@ describe('pushPayloadSchema', () => {
     expect(pushPayloadSchema.safeParse({ title: 'T' }).success).toBe(false);
     expect(pushPayloadSchema.safeParse({ body: 'B' }).success).toBe(false);
     expect(pushPayloadSchema.safeParse({ title: 'T', body: 'B', tag: 5 }).success).toBe(false);
+    expect(pushPayloadSchema.safeParse({ title: 'T', body: 'B', event: 'trip_invite' }).success).toBe(true);
+    expect(pushPayloadSchema.safeParse({ title: 'T', body: 'B', event: 1 }).success).toBe(false);
   });
 });

shared/src/notification/notification.schema.ts

@@ -125,5 +125,10 @@ export const pushPayloadSchema = z.object({
   body: z.string(),
   url: z.string().optional(),
   tag: z.string().optional(),
+  /**
+   * The event it reports (trip_invite, collab_message, ...). The Android app
+   * sorts notifications into its channels by it; a browser ignores it.
+   */
+  event: z.string().optional(),
 });
 export type PushPayload = z.infer<typeof pushPayloadSchema>;