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

packages/shared/src/utils.ts

@@ -114,4 +114,14 @@ export const API_ENDPOINTS = {
     bookmarkDetail: (id: string) => `/api/annotations/bookmarks/${id}/`,
     noteDetail: (id: string) => `/api/annotations/notes/${id}/`,
   },
+  groups: {
+    list: "/api/groups/",
+    detail: (id: number) => `/api/groups/${id}/`,
+    books: (groupId: number) => `/api/groups/${groupId}/books/`,
+    bookDetail: (groupId: number, bookId: number) => `/api/groups/${groupId}/books/${bookId}/`,
+    detectSections: (groupId: number, bookId: number) => `/api/groups/${groupId}/books/${bookId}/detect-sections/`,
+    adjustSections: (groupId: number, bookId: number) => `/api/groups/${groupId}/books/${bookId}/adjust-sections/`,
+    schedule: (groupId: number, bookId: number) => `/api/groups/${groupId}/books/${bookId}/schedule/`,
+    progress: (groupId: number, bookId: number) => `/api/groups/${groupId}/books/${bookId}/progress/`,
+  },
 } as const;