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/models.py

@@ -0,0 +1,161 @@
+from django.conf import settings
+from django.db import models
+
+from apps.books.models import EBook
+
+
+class ReadingGroup(models.Model):
+    """A reading group with an admin and members."""
+
+    name = models.CharField(max_length=256, db_index=True)
+    description = models.TextField(blank=True, default="")
+    admin = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        related_name="administered_groups",
+    )
+    members = models.ManyToManyField(
+        settings.AUTH_USER_MODEL,
+        through="ReadingGroupMembership",
+        related_name="reading_groups",
+    )
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "groups_reading_group"
+        verbose_name = "Reading Group"
+        verbose_name_plural = "Reading Groups"
+        ordering = ["-created_at"]
+
+    def __str__(self) -> str:
+        return self.name
+
+
+class ReadingGroupMembership(models.Model):
+    class Role(models.TextChoices):
+        ADMIN = "admin", "Admin"
+        MEMBER = "member", "Member"
+
+    user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
+    group = models.ForeignKey(ReadingGroup, on_delete=models.CASCADE, related_name="memberships")
+    role = models.CharField(max_length=16, choices=Role.choices, default=Role.MEMBER)
+    joined_at = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        db_table = "groups_membership"
+        unique_together = [("user", "group")]
+        verbose_name = "Reading Group Membership"
+        verbose_name_plural = "Reading Group Memberships"
+
+    def __str__(self) -> str:
+        return f"{self.user} in {self.group.name} ({self.role})"
+
+
+class GroupBook(models.Model):
+    """Links an uploaded EBook to a reading group."""
+
+    class Status(models.TextChoices):
+        ACTIVE = "active", "Active"
+        REPLACED = "replaced", "Replaced"
+
+    group = models.ForeignKey(
+        ReadingGroup, on_delete=models.CASCADE, related_name="group_books"
+    )
+    ebook = models.ForeignKey(
+        EBook, on_delete=models.CASCADE, related_name="group_books"
+    )
+    uploaded_by = models.ForeignKey(
+        settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name="uploaded_group_books"
+    )
+    title = models.CharField(max_length=512, db_index=True)
+    status = models.CharField(
+        max_length=16, choices=Status.choices, default=Status.ACTIVE, db_index=True
+    )
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "groups_group_book"
+        verbose_name = "Group Book"
+        verbose_name_plural = "Group Books"
+        ordering = ["-created_at"]
+        indexes = [models.Index(fields=["group", "status"])]
+
+    def __str__(self) -> str:
+        return f"{self.group.name} — {self.title}"
+
+
+class Section(models.Model):
+    """A section/chunk of a GroupBook for group reading."""
+
+    group_book = models.ForeignKey(
+        GroupBook, on_delete=models.CASCADE, related_name="sections"
+    )
+    title = models.CharField(max_length=512)
+    order = models.PositiveIntegerField(db_index=True)
+    start_chapter_index = models.PositiveIntegerField(default=0)
+    end_chapter_index = models.PositiveIntegerField(default=0)
+    estimated_reading_minutes = models.PositiveIntegerField(default=0)
+    created_at = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        db_table = "groups_section"
+        verbose_name = "Section"
+        verbose_name_plural = "Sections"
+        ordering = ["order"]
+        unique_together = [("group_book", "order")]
+        indexes = [models.Index(fields=["group_book", "order"])]
+
+    def __str__(self) -> str:
+        return f"{self.group_book.title} — Section {self.order}: {self.title}"
+
+
+class ReadingSchedule(models.Model):
+    """Reading schedule mapping sections to weekly meetings."""
+
+    group_book = models.ForeignKey(
+        GroupBook, on_delete=models.CASCADE, related_name="schedules"
+    )
+    meeting_number = models.PositiveIntegerField()
+    week_date = models.DateField()
+    section_ids = models.JSONField(default=list, help_text="Ordered list of Section IDs for this meeting")
+    created_at = models.DateTimeField(auto_now_add=True)
+
+    class Meta:
+        db_table = "groups_reading_schedule"
+        verbose_name = "Reading Schedule"
+        verbose_name_plural = "Reading Schedules"
+        ordering = ["meeting_number"]
+        unique_together = [("group_book", "meeting_number")]
+        indexes = [models.Index(fields=["group_book", "meeting_number"])]
+
+    def __str__(self) -> str:
+        return f"{self.group_book.title} — Meeting {self.meeting_number}"
+
+
+class MemberProgress(models.Model):
+    """Tracks a member's progress through sections of a group book."""
+
+    user = models.ForeignKey(
+        settings.AUTH_USER_MODEL, on_delete=models.CASCADE, related_name="group_progress"
+    )
+    group_book = models.ForeignKey(
+        GroupBook, on_delete=models.CASCADE, related_name="member_progress"
+    )
+    current_section = models.ForeignKey(
+        Section, on_delete=models.SET_NULL, null=True, blank=True, related_name="current_readers"
+    )
+    completed_sections = models.JSONField(
+        default=list, help_text="Ordered list of completed Section IDs"
+    )
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "groups_member_progress"
+        verbose_name = "Member Progress"
+        verbose_name_plural = "Member Progress"
+        unique_together = [("user", "group_book")]
+
+    def __str__(self) -> str:
+        return f"{self.user} — {self.group_book.title}"