feat: Update backend validation for 10-point rating scale

- Change rating validation from 1-5 to 1-10
- Enable half-star precision support in backend
- Maintain compatibility with frontend conversion logic
- Support odd numbers for half-star ratings (1,3,5,7,9)

internal/handlers/ebook.go

@@ -322,7 +322,7 @@ func (h *Handler) UpdateReadingProgress(c echo.Context) error {
 
 // CreateOrUpdateEbookRatingRequest represents the request for creating/updating an ebook rating
 type CreateOrUpdateEbookRatingRequest struct {
-	Rating int32 `json:"rating" validate:"required,min=1,max=5"`
+	Rating int32 `json:"rating" validate:"required,min=1,max=10"`
 }
 
 // GetEbookRating handles GET /api/ebooks/:id/rating