feat: add ntfy push notifications for daily digest and per-prayer reminders

- Server-side cron (node-cron) checks every minute for scheduled notifications
- Daily digest: sends all active prayers as a summary at a configured time
- Per-prayer reminders: pick days of the week per prayer; fires at configured time
- Settings panel in UI to configure ntfy topic, digest time, reminder time
- Test notification button to verify ntfy is working
- Settings stored in data/settings.json (persisted alongside prayers)

package.json

@@ -5,7 +5,8 @@
   "dependencies": {
     "cors": "^2.8.6",
     "docx": "^9.7.1",
-    "express": "^5.2.1"
+    "express": "^5.2.1",
+    "node-cron": "^4.6.0"
   },
   "devDependencies": {
     "@testing-library/dom": "^10.4.1",