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/serializers.py

@@ -1,6 +1,6 @@
 from rest_framework import serializers
 
-from apps.books.models import Book
+from apps.books.models import Book, Chapter, ReadingProgress
 
 
 class BookSerializer(serializers.ModelSerializer):
@@ -25,4 +25,47 @@ class BookListSerializer(serializers.ModelSerializer):
 
     class Meta:
         model = Book
-        fields = ["id", "title", "author", "total_pages", "cover_image"]
+        fields = ["id", "title", "author", "total_pages", "cover_image"]
+
+
+class ChapterSummarySerializer(serializers.ModelSerializer):
+    """Compact serializer for TOC listing — no content body."""
+
+    class Meta:
+        model = Chapter
+        fields = ["id", "book", "title", "number"]
+
+
+class ChapterDetailSerializer(serializers.ModelSerializer):
+    """Full serializer with chapter content for reading view."""
+
+    class Meta:
+        model = Chapter
+        fields = ["id", "book", "title", "number", "content", "created_at", "updated_at"]
+        read_only_fields = ["id", "created_at", "updated_at"]
+
+
+class ReadingProgressSerializer(serializers.ModelSerializer):
+    """Serialize reading progress for a book."""
+
+    class Meta:
+        model = ReadingProgress
+        fields = [
+            "id",
+            "book",
+            "current_chapter",
+            "current_position",
+            "percentage",
+            "updated_at",
+        ]
+        read_only_fields = ["id", "updated_at"]
+
+    def validate_percentage(self, value: float) -> float:
+        if value < 0.0 or value > 100.0:
+            raise serializers.ValidationError("Percentage must be between 0 and 100.")
+        return value
+
+    def validate_current_chapter(self, value: int) -> int:
+        if value < 1:
+            raise serializers.ValidationError("Chapter number must be positive.")
+        return value