feat(packs): PackImporter stubs pass + IsEnabled gate in active-packs

PackImporter now runs a second pass over pack-stubs.json, inserting
PackConfigEntry placeholders for any pack_id NOT already present from
the live-capture packs.json pass. Synthesized stubs default
IsEnabled=false; live-capture rows default IsEnabled=true.

PackRepository.GetActivePacks filters by IsEnabled in addition to the
date window, so synthesized stubs stay hidden until an operator opts
them in (UPDATE Packs SET IsEnabled=true WHERE Id=...).

Bundles Task 6 + Task 11 because adding pack-stubs.json to the
test-fixture set surfaces an extra row in PackControllerFullCatalogTests'
35-pack count assertion; the filter is what makes the test resilient.

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

SVSim.UnitTests/Importers/PackImporterStubsTests.cs

@@ -0,0 +1,44 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using SVSim.Bootstrap.Importers;
+using SVSim.Database;
+using SVSim.UnitTests.Infrastructure;
+
+namespace SVSim.UnitTests.Importers;
+
+public class PackImporterStubsTests
+{
+    private static string SeedDir => Path.Combine(AppContext.BaseDirectory, "Data", "seeds");
+
+    [Test]
+    public async Task Live_capture_overrides_stub_on_conflict()
+    {
+        using var factory = new SVSimTestFactory();
+        using var scope = factory.Services.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+
+        await new PackImporter().ImportAsync(db, SeedDir);
+
+        // 10001 is in both packs.json (no is_enabled -> defaults true) and pack-stubs.json
+        // (is_enabled=false). Live capture wins -> IsEnabled stays true and gacha_detail
+        // is the packs.json value, not "STUB CLC".
+        var live = await db.Packs.FirstAsync(p => p.Id == 10001);
+        Assert.That(live.IsEnabled, Is.True);
+        Assert.That(live.GachaDetail, Does.Not.Contain("STUB"));
+    }
+
+    [Test]
+    public async Task Stub_only_packs_are_inserted_with_IsEnabled_false()
+    {
+        using var factory = new SVSimTestFactory();
+        using var scope = factory.Services.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+
+        await new PackImporter().ImportAsync(db, SeedDir);
+
+        // 95001 is stub-only -> inserted with IsEnabled=false and the stub's gacha_detail.
+        var stub = await db.Packs.FirstAsync(p => p.Id == 95001);
+        Assert.That(stub.IsEnabled, Is.False);
+        Assert.That(stub.GachaDetail, Is.EqualTo("7th Anniv stub"));
+    }
+}