Add Columbia Coatings catalog integration schema fields

Phase 1a of the Columbia Coatings API integration. Adds the persisted
fields the sync/mapper will need, ahead of the client and sync service:

PowderCatalogItem:
- Category: our product category (e.g. "Powder Additives" for gram-sold
  pigments) derived from vendor taxonomy at import, not stored raw.
- Source: provenance (e.g. "Columbia Coatings API"), kept separate from
  VendorName (= derived manufacturer) so a distributor's right-to-delete
  can purge by feed regardless of manufacturer.
- ChemistryType: resin chemistry (Polyester/TGIC/Epoxy/...), distinct
  from Finish.
- MilThickness: recommended film build as vendor free text.
- CureScheduleText: raw cure schedule verbatim (formats vary widely).
- CureCurvesJson: all parsed cure curves, so alternate low-temp curves
  are preserved for heat-sensitive substrates, not just the primary.
- FormulationChanges: vendor reformulation log; a signal cure specs may
  have changed.

InventoryItem:
- PowderCatalogItemId: loose link to the catalog row (matches the
  QuoteItemCoat pattern) so inventory detail can show manufacturer-level
  status (e.g. discontinued/cannot reorder) and future change flags.
  Nulled, never cascaded, when source catalog data is purged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/PowderCoating.Infrastructure/Migrations/ApplicationDbContextModelSnapshot.cs

@@ -4173,6 +4173,9 @@ namespace PowderCoating.Infrastructure.Migrations
                     b.Property<string>("Notes")
                         .HasColumnType("nvarchar(max)");
 
+                    b.Property<int?>("PowderCatalogItemId")
+                        .HasColumnType("int");
+
                     b.Property<int?>("PrimaryVendorId")
                         .HasColumnType("int");
 
@@ -6936,6 +6939,12 @@ namespace PowderCoating.Infrastructure.Migrations
                     b.Property<string>("ApplicationGuideUrl")
                         .HasColumnType("nvarchar(max)");
 
+                    b.Property<string>("Category")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("ChemistryType")
+                        .HasColumnType("nvarchar(max)");
+
                     b.Property<string>("ColorFamilies")
                         .HasColumnType("nvarchar(max)");
 
@@ -6949,6 +6958,12 @@ namespace PowderCoating.Infrastructure.Migrations
                     b.Property<DateTime>("CreatedAt")
                         .HasColumnType("datetime2");
 
+                    b.Property<string>("CureCurvesJson")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("CureScheduleText")
+                        .HasColumnType("nvarchar(max)");
+
                     b.Property<decimal?>("CureTemperatureF")
                         .HasColumnType("decimal(18,2)");
 
@@ -6961,6 +6976,9 @@ namespace PowderCoating.Infrastructure.Migrations
                     b.Property<string>("Finish")
                         .HasColumnType("nvarchar(max)");
 
+                    b.Property<string>("FormulationChanges")
+                        .HasColumnType("nvarchar(max)");
+
                     b.Property<string>("ImageUrl")
                         .HasColumnType("nvarchar(max)");
 
@@ -6973,6 +6991,9 @@ namespace PowderCoating.Infrastructure.Migrations
                     b.Property<DateTime?>("LastSyncedAt")
                         .HasColumnType("datetime2");
 
+                    b.Property<string>("MilThickness")
+                        .HasColumnType("nvarchar(max)");
+
                     b.Property<string>("PriceTiersJson")
                         .HasColumnType("nvarchar(max)");
 
@@ -6989,6 +7010,9 @@ namespace PowderCoating.Infrastructure.Migrations
                         .IsRequired()
                         .HasColumnType("nvarchar(450)");
 
+                    b.Property<string>("Source")
+                        .HasColumnType("nvarchar(max)");
+
                     b.Property<decimal?>("SpecificGravity")
                         .HasColumnType("decimal(18,2)");
 
@@ -7210,7 +7234,7 @@ namespace PowderCoating.Infrastructure.Migrations
                         {
                             Id = 1,
                             CompanyId = 0,
-                            CreatedAt = new DateTime(2026, 6, 14, 1, 21, 46, 131, DateTimeKind.Utc).AddTicks(4191),
+                            CreatedAt = new DateTime(2026, 6, 17, 14, 21, 27, 126, DateTimeKind.Utc).AddTicks(6644),
                             Description = "Standard pricing for regular customers",
                             DiscountPercent = 0m,
                             IsActive = true,
@@ -7221,7 +7245,7 @@ namespace PowderCoating.Infrastructure.Migrations
                         {
                             Id = 2,
                             CompanyId = 0,
-                            CreatedAt = new DateTime(2026, 6, 14, 1, 21, 46, 131, DateTimeKind.Utc).AddTicks(4196),
+                            CreatedAt = new DateTime(2026, 6, 17, 14, 21, 27, 126, DateTimeKind.Utc).AddTicks(6651),
                             Description = "5% discount for preferred customers",
                             DiscountPercent = 5m,
                             IsActive = true,
@@ -7232,7 +7256,7 @@ namespace PowderCoating.Infrastructure.Migrations
                         {
                             Id = 3,
                             CompanyId = 0,
-                            CreatedAt = new DateTime(2026, 6, 14, 1, 21, 46, 131, DateTimeKind.Utc).AddTicks(4197),
+                            CreatedAt = new DateTime(2026, 6, 17, 14, 21, 27, 126, DateTimeKind.Utc).AddTicks(6652),
                             Description = "10% discount for premium customers",
                             DiscountPercent = 10m,
                             IsActive = true,