feat(inventory): GrantAsync handles cosmetic branches

Sleeve/Emblem/Skin/Degree/MyPageBG grants are idempotent on the viewer's
owned-collection but always emit a wire entry at the top level (preserves
"+1 sleeve" purchase popup). Unknown ids throw InventoryCatalogException.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.UnitTests/Services/Inventory/InventoryGrantCosmeticTests.cs

@@ -0,0 +1,69 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using SVSim.Database;
+using SVSim.Database.Enums;
+using SVSim.Database.Models;
+using SVSim.Database.Services.Inventory;
+using SVSim.UnitTests.Infrastructure;
+
+namespace SVSim.UnitTests.Services.Inventory;
+
+public class InventoryGrantCosmeticTests
+{
+    [Test]
+    public async Task Sleeve_added_when_missing()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        using var scope = factory.Services.CreateScope();
+        var ctx = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+        const int sleeveId = 2_000_000_001;
+        ctx.Sleeves.Add(new SleeveEntry { Id = sleeveId });
+        await ctx.SaveChangesAsync();
+
+        var inv = scope.ServiceProvider.GetRequiredService<IInventoryService>();
+        await using var tx = await inv.BeginAsync(viewerId);
+        var granted = await tx.GrantAsync(UserGoodsType.Sleeve, sleeveId, 1);
+
+        Assert.That(granted, Has.Count.EqualTo(1));
+        Assert.That(granted[0].RewardType, Is.EqualTo((int)UserGoodsType.Sleeve));
+        Assert.That(granted[0].RewardId, Is.EqualTo(sleeveId));
+        Assert.That(granted[0].RewardNum, Is.EqualTo(1));
+        Assert.That(tx.Viewer.Sleeves.Any(s => s.Id == sleeveId), Is.True);
+    }
+
+    [Test]
+    public async Task Sleeve_idempotent_when_already_owned_but_still_emits_entry()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        using var scope = factory.Services.CreateScope();
+        var ctx = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+        const int sleeveId = 2_000_000_002;
+        var sleeve = new SleeveEntry { Id = sleeveId };
+        ctx.Sleeves.Add(sleeve);
+        var v = await ctx.Viewers.Include(x => x.Sleeves).FirstAsync(x => x.Id == viewerId);
+        v.Sleeves.Add(sleeve);
+        await ctx.SaveChangesAsync();
+
+        var inv = scope.ServiceProvider.GetRequiredService<IInventoryService>();
+        await using var tx = await inv.BeginAsync(viewerId);
+        var granted = await tx.GrantAsync(UserGoodsType.Sleeve, sleeveId, 1);
+
+        Assert.That(granted, Has.Count.EqualTo(1), "top-level cosmetic grant emits even if owned");
+        Assert.That(tx.Viewer.Sleeves.Count(s => s.Id == sleeveId), Is.EqualTo(1), "no duplicate row");
+    }
+
+    [Test]
+    public async Task Unknown_cosmetic_id_throws_catalog_exception()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        using var scope = factory.Services.CreateScope();
+        var inv = scope.ServiceProvider.GetRequiredService<IInventoryService>();
+        await using var tx = await inv.BeginAsync(viewerId);
+
+        Assert.ThrowsAsync<InventoryCatalogException>(
+            async () => { await tx.GrantAsync(UserGoodsType.Sleeve, 999_999, 1); });
+    }
+}