Add vendor supply categories with inventory auto-filter

Vendors can now be tagged with one or more inventory categories (Powder,
Chemical, etc.) via checkboxes on the Create/Edit form. The inventory
Create/Edit vendor dropdown automatically filters to matching vendors when
a category is selected; falls back to all vendors if none are tagged.
Includes migration AddVendorCategories (VendorInventoryCategories join table).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Infrastructure/Data/ApplicationDbContext.cs

@@ -809,6 +809,15 @@ modelBuilder.Entity<ReworkRecord>().HasQueryFilter(e =>
             .HasForeignKey(s => s.DefaultExpenseAccountId)
             .OnDelete(DeleteBehavior.SetNull);
 
+        // Vendor ↔ InventoryCategoryLookup (many-to-many supply categories)
+        modelBuilder.Entity<Vendor>()
+            .HasMany(v => v.Categories)
+            .WithMany(c => c.Vendors)
+            .UsingEntity<Dictionary<string, object>>(
+                "VendorInventoryCategories",
+                j => j.HasOne<InventoryCategoryLookup>().WithMany().HasForeignKey("InventoryCategoryLookupId"),
+                j => j.HasOne<Vendor>().WithMany().HasForeignKey("VendorId"));
+
         // Bill → APAccount (no cascade to avoid cycles)
         modelBuilder.Entity<Bill>()
             .HasOne(b => b.APAccount)

src/PowderCoating.Infrastructure/Migrations/20260523135110_AddVendorCategories.cs

@@ -0,0 +1,93 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace PowderCoating.Infrastructure.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddVendorCategories : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "VendorInventoryCategories",
+                columns: table => new
+                {
+                    InventoryCategoryLookupId = table.Column<int>(type: "int", nullable: false),
+                    VendorId = table.Column<int>(type: "int", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_VendorInventoryCategories", x => new { x.InventoryCategoryLookupId, x.VendorId });
+                    table.ForeignKey(
+                        name: "FK_VendorInventoryCategories_InventoryCategoryLookups_InventoryCategoryLookupId",
+                        column: x => x.InventoryCategoryLookupId,
+                        principalTable: "InventoryCategoryLookups",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Cascade);
+                    table.ForeignKey(
+                        name: "FK_VendorInventoryCategories_Vendors_VendorId",
+                        column: x => x.VendorId,
+                        principalTable: "Vendors",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Cascade);
+                });
+
+            migrationBuilder.UpdateData(
+                table: "PricingTiers",
+                keyColumn: "Id",
+                keyValue: 1,
+                column: "CreatedAt",
+                value: new DateTime(2026, 5, 23, 13, 51, 6, 293, DateTimeKind.Utc).AddTicks(4300));
+
+            migrationBuilder.UpdateData(
+                table: "PricingTiers",
+                keyColumn: "Id",
+                keyValue: 2,
+                column: "CreatedAt",
+                value: new DateTime(2026, 5, 23, 13, 51, 6, 293, DateTimeKind.Utc).AddTicks(4313));
+
+            migrationBuilder.UpdateData(
+                table: "PricingTiers",
+                keyColumn: "Id",
+                keyValue: 3,
+                column: "CreatedAt",
+                value: new DateTime(2026, 5, 23, 13, 51, 6, 293, DateTimeKind.Utc).AddTicks(4315));
+
+            migrationBuilder.CreateIndex(
+                name: "IX_VendorInventoryCategories_VendorId",
+                table: "VendorInventoryCategories",
+                column: "VendorId");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "VendorInventoryCategories");
+
+            migrationBuilder.UpdateData(
+                table: "PricingTiers",
+                keyColumn: "Id",
+                keyValue: 1,
+                column: "CreatedAt",
+                value: new DateTime(2026, 5, 21, 14, 32, 24, 337, DateTimeKind.Utc).AddTicks(8533));
+
+            migrationBuilder.UpdateData(
+                table: "PricingTiers",
+                keyColumn: "Id",
+                keyValue: 2,
+                column: "CreatedAt",
+                value: new DateTime(2026, 5, 21, 14, 32, 24, 337, DateTimeKind.Utc).AddTicks(8542));
+
+            migrationBuilder.UpdateData(
+                table: "PricingTiers",
+                keyColumn: "Id",
+                keyValue: 3,
+                column: "CreatedAt",
+                value: new DateTime(2026, 5, 21, 14, 32, 24, 337, DateTimeKind.Utc).AddTicks(8543));
+        }
+    }
+}

src/PowderCoating.Infrastructure/Migrations/ApplicationDbContextModelSnapshot.cs

@@ -6711,7 +6711,7 @@ namespace PowderCoating.Infrastructure.Migrations
                         {
                             Id = 1,
                             CompanyId = 0,
-                            CreatedAt = new DateTime(2026, 5, 21, 14, 32, 24, 337, DateTimeKind.Utc).AddTicks(8533),
+                            CreatedAt = new DateTime(2026, 5, 23, 13, 51, 6, 293, DateTimeKind.Utc).AddTicks(4300),
                             Description = "Standard pricing for regular customers",
                             DiscountPercent = 0m,
                             IsActive = true,
@@ -6722,7 +6722,7 @@ namespace PowderCoating.Infrastructure.Migrations
                         {
                             Id = 2,
                             CompanyId = 0,
-                            CreatedAt = new DateTime(2026, 5, 21, 14, 32, 24, 337, DateTimeKind.Utc).AddTicks(8542),
+                            CreatedAt = new DateTime(2026, 5, 23, 13, 51, 6, 293, DateTimeKind.Utc).AddTicks(4313),
                             Description = "5% discount for preferred customers",
                             DiscountPercent = 5m,
                             IsActive = true,
@@ -6733,7 +6733,7 @@ namespace PowderCoating.Infrastructure.Migrations
                         {
                             Id = 3,
                             CompanyId = 0,
-                            CreatedAt = new DateTime(2026, 5, 21, 14, 32, 24, 337, DateTimeKind.Utc).AddTicks(8543),
+                            CreatedAt = new DateTime(2026, 5, 23, 13, 51, 6, 293, DateTimeKind.Utc).AddTicks(4315),
                             Description = "10% discount for premium customers",
                             DiscountPercent = 10m,
                             IsActive = true,
@@ -8634,6 +8634,21 @@ namespace PowderCoating.Infrastructure.Migrations
                     b.ToTable("YearEndCloses");
                 });
 
+            modelBuilder.Entity("VendorInventoryCategories", b =>
+                {
+                    b.Property<int>("InventoryCategoryLookupId")
+                        .HasColumnType("int");
+
+                    b.Property<int>("VendorId")
+                        .HasColumnType("int");
+
+                    b.HasKey("InventoryCategoryLookupId", "VendorId");
+
+                    b.HasIndex("VendorId");
+
+                    b.ToTable("VendorInventoryCategories");
+                });
+
             modelBuilder.Entity("Microsoft.AspNetCore.Identity.IdentityRoleClaim<string>", b =>
                 {
                     b.HasOne("Microsoft.AspNetCore.Identity.IdentityRole", null)
@@ -10372,6 +10387,21 @@ namespace PowderCoating.Infrastructure.Migrations
                     b.Navigation("JournalEntry");
                 });
 
+            modelBuilder.Entity("VendorInventoryCategories", b =>
+                {
+                    b.HasOne("PowderCoating.Core.Entities.InventoryCategoryLookup", null)
+                        .WithMany()
+                        .HasForeignKey("InventoryCategoryLookupId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.HasOne("PowderCoating.Core.Entities.Vendor", null)
+                        .WithMany()
+                        .HasForeignKey("VendorId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+                });
+
             modelBuilder.Entity("PowderCoating.Core.Entities.Account", b =>
                 {
                     b.Navigation("BillLineItems");