Store powder specific gravity and fix coverage math

src/PowderCoating.Application/DTOs/Inventory/InventoryDtos.cs

@@ -17,6 +17,7 @@ public class InventoryItemDto
     public string? Manufacturer { get; set; }
     public string? ManufacturerPartNumber { get; set; }
     public decimal? CoverageSqFtPerLb { get; set; }
+    public decimal? SpecificGravity { get; set; }
     public decimal? TransferEfficiency { get; set; }
     public int? CureTemperatureF { get; set; }
     public int? CureTimeMinutes { get; set; }
@@ -125,6 +126,10 @@ public class CreateInventoryItemDto
     [Display(Name = "Coverage (Sq Ft/Lb)")]
     public decimal? CoverageSqFtPerLb { get; set; }
 
+    [Range(0, 100, ErrorMessage = "Specific gravity must be between 0 and 100")]
+    [Display(Name = "Specific Gravity")]
+    public decimal? SpecificGravity { get; set; }
+
     [Range(0, 100, ErrorMessage = "Transfer efficiency must be between 0 and 100%")]
     [Display(Name = "Transfer Efficiency (%)")]
     public decimal? TransferEfficiency { get; set; }

src/PowderCoating.Application/DTOs/Inventory/PowderCatalogDtos.cs

@@ -23,6 +23,7 @@ public class PowderCatalogLookupResult
     public string? ColorFamilies { get; set; }
     public bool? RequiresClearCoat { get; set; }
     public decimal? CoverageSqFtPerLb { get; set; }
+    public decimal? SpecificGravity { get; set; }
     public decimal? TransferEfficiency { get; set; }
 }