feat: implement reading pace notifications (US #33)

Backend:
- New hermes app with ReadingGroup, GroupMeeting, GroupMembership models
- NotificationPreference (per-user: enable/disable, frequency daily/weekly)
- PaceNotification model for tracking sent/dismissed notifications
- Pace calculation service comparing current progress vs meeting targets
- API endpoints: pace status, notification preferences CRUD, reminders, dismiss
- Ahead/behind/on_track/completed status determination

Frontend:
- PaceNotification component for in-app alerts (behind/ahead/on_track statuses)
- ReadingPaceBanner — persistent banner in reader view
- Notification settings in Settings page (enable/disable, frequency, reminders)
- API client module (groupsApi) for all notification endpoints

backend/apps/groups/admin.py

@@ -0,0 +1,38 @@
+from django.contrib import admin
+
+from apps.groups.models import (
+    GroupMeeting,
+    GroupMembership,
+    NotificationPreference,
+    PaceNotification,
+    ReadingGroup,
+)
+
+
+@admin.register(ReadingGroup)
+class ReadingGroupAdmin(admin.ModelAdmin):
+    list_display = ["name", "created_by", "created_at"]
+    search_fields = ["name"]
+
+
+@admin.register(GroupMembership)
+class GroupMembershipAdmin(admin.ModelAdmin):
+    list_display = ["user", "group", "role", "joined_at"]
+    list_filter = ["role"]
+
+
+@admin.register(GroupMeeting)
+class GroupMeetingAdmin(admin.ModelAdmin):
+    list_display = ["group", "title", "target_section_label", "scheduled_at"]
+    list_filter = ["group"]
+
+
+@admin.register(NotificationPreference)
+class NotificationPreferenceAdmin(admin.ModelAdmin):
+    list_display = ["user", "pace_notifications_enabled", "reminder_enabled", "frequency"]
+
+
+@admin.register(PaceNotification)
+class PaceNotificationAdmin(admin.ModelAdmin):
+    list_display = ["user", "meeting", "status", "created_at"]
+    list_filter = ["status"]