feat: customizable mobile reading experience

- Backend: Chapter, ReadingProgress, ReadingSettings models
- Backend: Chapter API (TOC + content), progress tracking, settings CRUD
- Frontend: ReadingPage with chapter navigation
- Frontend: TableOfContents drawer
- Frontend: ReadingSettingsPanel (theme, font, size, orientation)
- Frontend: Custom hooks for settings, chapters, progress tracking
- CSS: Mobile-first reading view with sepia/dark/light/paper themes
- Route: /reader/:bookId reading view from book detail page
- Docs: 001-customizable-mobile-reading-experience.md

backend/apps/books/models.py

@@ -18,4 +18,71 @@ class Book(models.Model):
         ordering = ["title"]
 
     def __str__(self) -> str:
-        return self.title
+        return self.title
+
+
+class Chapter(models.Model):
+    """A chapter within a book, containing the text/markdown content."""
+
+    book = models.ForeignKey(
+        Book,
+        on_delete=models.CASCADE,
+        related_name="chapters",
+        db_index=True,
+    )
+    title = models.CharField(max_length=512)
+    number = models.PositiveIntegerField()
+    content = models.TextField(blank=True, default="")
+    created_at = models.DateTimeField(auto_now_add=True)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "books_chapter"
+        verbose_name = "Chapter"
+        verbose_name_plural = "Chapters"
+        ordering = ["book", "number"]
+        constraints = [
+            models.UniqueConstraint(
+                fields=["book", "number"],
+                name="uq_book_chapter_number",
+            )
+        ]
+
+    def __str__(self) -> str:
+        return f"{self.book.title} — Ch. {self.number}: {self.title}"
+
+
+class ReadingProgress(models.Model):
+    """Tracks a user's reading progress within a book."""
+
+    user = models.ForeignKey(
+        "users.User",
+        on_delete=models.CASCADE,
+        related_name="reading_progress",
+        db_index=True,
+    )
+    book = models.ForeignKey(
+        Book,
+        on_delete=models.CASCADE,
+        related_name="reading_progress",
+        db_index=True,
+    )
+    current_chapter = models.PositiveIntegerField(default=1)
+    current_position = models.PositiveIntegerField(default=0)
+    percentage = models.FloatField(default=0.0)
+    updated_at = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        db_table = "books_reading_progress"
+        verbose_name = "Reading Progress"
+        verbose_name_plural = "Reading Progress"
+        ordering = ["-updated_at"]
+        constraints = [
+            models.UniqueConstraint(
+                fields=["user", "book"],
+                name="uq_reading_progress_user_book",
+            )
+        ]
+
+    def __str__(self) -> str:
+        return f"{self.user} — {self.book.title} ({self.percentage:.0f}%)"