feat: Add auto-sync, fix partner linking UI, update sharing settings

- Add 10-second periodic auto-sync to CycleEntriesNotifier
- Fix husband_devotional_screen: use partnerId for isConnected check, navigate to SharingSettingsScreen instead of legacy mock dialog
- Remove obsolete _showConnectDialog method and mock data import
- Update husband_settings_screen: show 'Partner Settings' with linked partner name when connected
- Add SharingSettingsScreen: Pad Supplies toggle (disabled when pad tracking off), Intimacy always enabled
- Add CORS OPTIONS handler to backend server
- Add _ensureServerRegistration for reliable partner linking
- Add copy button to Invite Partner dialog
- Dynamic base URL for web (uses window.location.hostname)

lib/providers/teaching_plan_provider.dart

@@ -0,0 +1,39 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:hive_flutter/hive_flutter.dart';
+import '../models/teaching_plan.dart';
+
+final teachingPlansProvider =
+    StateNotifierProvider<TeachingPlansNotifier, List<TeachingPlan>>((ref) {
+  return TeachingPlansNotifier();
+});
+
+class TeachingPlansNotifier extends StateNotifier<List<TeachingPlan>> {
+  TeachingPlansNotifier() : super([]) {
+    _loadPlans();
+  }
+
+  void _loadPlans() {
+    if (Hive.isBoxOpen('teaching_plans_v2')) {
+      final box = Hive.box<TeachingPlan>('teaching_plans_v2');
+      state = box.values.toList()..sort((a, b) => b.date.compareTo(a.date));
+    }
+  }
+
+  Future<void> addPlan(TeachingPlan plan) async {
+    final box = Hive.box<TeachingPlan>('teaching_plans_v2');
+    await box.put(plan.id, plan);
+    _loadPlans();
+  }
+
+  Future<void> updatePlan(TeachingPlan plan) async {
+    final box = Hive.box<TeachingPlan>('teaching_plans_v2');
+    await box.put(plan.id, plan);
+    _loadPlans();
+  }
+
+  Future<void> deletePlan(String id) async {
+    final box = Hive.box<TeachingPlan>('teaching_plans_v2');
+    await box.delete(id);
+    _loadPlans();
+  }
+}