feat(debug): expose nextEligibleAt and structured send-wakeup results

Extend authenticated debug endpoints for local iOS notification testing:
add nextEligibleAt (23h prod / 10m test) to device lookup, return success
and failureReason from send-wakeup with masked tokens only, reuse
resolveOwnedDevice for ownership checks, and standardize [DebugEndpoint] logs.

src/services/pushService.ts

@@ -5,10 +5,22 @@ import { messaging } from "./firebase.js";
 const MS_PRODUCTION = 23 * 60 * 60 * 1000;
 const MS_TEST = 10 * 60 * 1000;
 
-function notifyThresholdMs(testMode?: boolean): number {
+export function notifyThresholdMs(testMode?: boolean): number {
   return testMode === true ? MS_TEST : MS_PRODUCTION;
 }
 
+/** Epoch ms when the device may receive another push (diagnostics only). */
+export function computeNextEligibleAt(row: {
+  lastNotifiedAt?: number;
+  testMode?: boolean;
+}): number {
+  const threshold = notifyThresholdMs(row.testMode);
+  if (row.lastNotifiedAt === undefined) {
+    return Date.now();
+  }
+  return row.lastNotifiedAt + threshold;
+}
+
 function lastNotifiedMs(row: StoredRow | undefined): number | undefined {
   const v = row?.lastNotifiedAt;
   if (v === undefined) return undefined;