docs: Add Push Notification Permission UI task to backlog

- Added task #16: Push Notification Permission UI (5-7 hours total)
  * Frontend: Permission request component (2-3 hours)
  * Backend: Firebase FCM integration (3-4 hours)
  * This is the remaining 5% of PWA features

- Renumbered subsequent tasks (17-21)
- Updated totals: 21 tasks, 45-70 hours estimated

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

docs/BACKLOG.md

@@ -336,9 +336,46 @@ interface UserState {
 
 ---
 
+### 16. Push Notification Permission UI
+**Status**: Not Started
+**Estimated Effort**: 2-3 hours (Frontend) + 3-4 hours (Backend)
+**Priority**: Low (Post-Launch)
+**Related**: PWA Features (95% complete, this is the remaining 5%)
+
+**Description**: Implement web push notification permission request and backend Firebase FCM integration.
+
+**Frontend Requirements**:
+- [ ] Create PushNotificationPermission component
+- [ ] Request notification permission from browser
+- [ ] Handle permission states (granted, denied, default)
+- [ ] Send FCM token to backend when granted
+- [ ] Show permission prompt at appropriate time (not immediately)
+- [ ] Store permission state in user preferences
+
+**Backend Requirements**:
+- [ ] Firebase Cloud Messaging (FCM) integration
+- [ ] Store FCM tokens per user/device
+- [ ] Create notification sending service
+- [ ] Add endpoints: POST /notifications/subscribe, DELETE /notifications/unsubscribe
+- [ ] Implement notification templates (activity reminders, family updates)
+- [ ] Handle token refresh and cleanup
+
+**Files to Create**:
+- Frontend: `components/pwa/PushNotificationPermission.tsx`
+- Backend: `src/modules/notifications/fcm.service.ts`
+- Backend: `src/modules/notifications/push-notification.service.ts`
+
+**Implementation Notes**:
+- Requires Firebase project setup
+- Need VAPID keys for web push
+- Test on multiple browsers (Chrome, Firefox, Safari)
+- iOS requires PWA installed for push notifications
+
+---
+
 ## 📋 Future Features
 
-### 16. Offline Mode Enhancements
+### 17. Offline Mode Enhancements
 **Status**: Basic offline support exists
 **Estimated Effort**: 6-8 hours
 **Priority**: Medium
@@ -352,7 +389,7 @@ interface UserState {
 
 ---
 
-### 17. Voice Input Multi-Language Support
+### 18. Voice Input Multi-Language Support
 **Status**: Works with backend language detection
 **Estimated Effort**: 2-3 hours
 **Priority**: Low
@@ -365,7 +402,7 @@ interface UserState {
 
 ---
 
-### 18. Export/Import Data
+### 19. Export/Import Data
 **Status**: Not Started
 **Estimated Effort**: 4-6 hours
 **Priority**: Medium
@@ -379,7 +416,7 @@ interface UserState {
 
 ---
 
-### 19. Dark Mode
+### 20. Dark Mode
 **Status**: Not Started
 **Estimated Effort**: 3-4 hours
 **Priority**: Low
@@ -393,7 +430,7 @@ interface UserState {
 
 ---
 
-### 20. Push Notifications Localization
+### 21. Push Notifications Localization
 **Status**: Backend supports multi-language
 **Estimated Effort**: 2-3 hours
 **Priority**: Medium
@@ -408,12 +445,12 @@ interface UserState {
 
 ## 📊 Progress Tracking
 
-**Total Tasks**: 20
+**Total Tasks**: 21
 **High Priority**: 3 tasks (15%)
 **Medium Priority**: 3 tasks (15%)
-**Low Priority**: 14 tasks (70%)
+**Low Priority**: 15 tasks (71%)
 
-**Estimated Total Effort**: 40-60 hours (1-1.5 weeks)
+**Estimated Total Effort**: 45-70 hours (1-1.75 weeks)
 
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