feat: implement group EPUB upload and section splitting (US #29)

Backend:
- Create hermes Django app with models: ReadingGroup, GroupBook, Section, ReadingSchedule, MemberProgress
- EPUB section splitting service with automatic detection and reading time estimation
- Section recommendation engine for 4-week meeting schedule
- REST API endpoints for groups, books, sections, schedule, and member progress
- Manual section adjustment (merge/split) support

Frontend:
- GroupsPage: list/create reading groups
- GroupDetailPage: manage members, upload EPUB to group, view group books
- GroupBookPage: section breakdown with merge/split controls, reading schedule, member progress
- API client and TypeScript types for all group operations
- i18n keys for English and Spanish

Shared:
- Group-related types and API endpoint constants in packages/shared

backend/apps/groups/admin.py

@@ -0,0 +1,46 @@
+from django.contrib import admin
+
+from apps.groups.models import (
+    GroupBook,
+    MemberProgress,
+    ReadingGroup,
+    ReadingGroupMembership,
+    ReadingSchedule,
+    Section,
+)
+
+
+@admin.register(ReadingGroup)
+class ReadingGroupAdmin(admin.ModelAdmin):
+    list_display = ["name", "admin", "created_at"]
+    search_fields = ["name", "admin__email"]
+
+
+@admin.register(ReadingGroupMembership)
+class ReadingGroupMembershipAdmin(admin.ModelAdmin):
+    list_display = ["user", "group", "role", "joined_at"]
+    list_filter = ["role", "group"]
+
+
+@admin.register(GroupBook)
+class GroupBookAdmin(admin.ModelAdmin):
+    list_display = ["title", "group", "status", "uploaded_by", "created_at"]
+    list_filter = ["status"]
+    search_fields = ["title", "group__name"]
+
+
+@admin.register(Section)
+class SectionAdmin(admin.ModelAdmin):
+    list_display = ["title", "group_book", "order", "estimated_reading_minutes"]
+    ordering = ["group_book", "order"]
+
+
+@admin.register(ReadingSchedule)
+class ReadingScheduleAdmin(admin.ModelAdmin):
+    list_display = ["group_book", "meeting_number", "week_date"]
+    ordering = ["group_book", "meeting_number"]
+
+
+@admin.register(MemberProgress)
+class MemberProgressAdmin(admin.ModelAdmin):
+    list_display = ["user", "group_book", "current_section", "updated_at"]