refactor(bootstrap): migrate practice opponents to seed file

Move /practice/info handling out of GlobalsImporter into a dedicated
PracticeOpponentImporter that reads a normalized JSON seed file
generated by data_dumps/extract/extract-practice-opponents.ps1.

SVSim.UnitTests/Importers/PracticeOpponentImporterTests.cs

@@ -0,0 +1,41 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using SVSim.Bootstrap.Importers;
+using SVSim.Database;
+using SVSim.UnitTests.Infrastructure;
+
+namespace SVSim.UnitTests.Importers;
+
+public class PracticeOpponentImporterTests
+{
+    private static string SeedDir => Path.Combine(AppContext.BaseDirectory, "Data", "seeds");
+
+    [Test]
+    public async Task Imports_opponents_from_seed_file()
+    {
+        using var factory = new SVSimTestFactory();
+        using var scope = factory.Services.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+
+        await new PracticeOpponentImporter().ImportAsync(db, SeedDir);
+
+        var opponents = await db.PracticeOpponents.OrderBy(p => p.Id).ToListAsync();
+        Assert.That(opponents.Count, Is.GreaterThan(0), "seed file must contain opponents");
+        Assert.That(opponents.All(o => o.ClassId >= 0), Is.True);
+    }
+
+    [Test]
+    public async Task Is_idempotent_on_rerun()
+    {
+        using var factory = new SVSimTestFactory();
+        using var scope = factory.Services.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+
+        await new PracticeOpponentImporter().ImportAsync(db, SeedDir);
+        int before = await db.PracticeOpponents.CountAsync();
+        await new PracticeOpponentImporter().ImportAsync(db, SeedDir);
+        int after = await db.PracticeOpponents.CountAsync();
+
+        Assert.That(after, Is.EqualTo(before));
+    }
+}