Phase 7: Tests erweitert + Mongo-Parser extrahiert (testbar)

Tests (jetzt 48 grün):
- DbContextMappingTests: sichert core_/mod_-Tabellennamen, Position-Composite-Key,
  TrackedTrader-Key, ClosedTradeRow nicht gemappt, AccountState.OpenPositions ignoriert.
- PositionRepositoryTests: Live/Demo-Trennung, Upsert setzt Account+Demo-Flag,
  Update ohne Duplikat, DeleteLive, DropDemo.
- MarketRepositoryTests: GetActive filtert Closed, Upsert-Update, FindByTokenId.
- TradeLogRepositoryTests: GetRecent (Sortierung+Limit), Find-Predikat, Guid-Id unique.
- MongoExportParserTests: String-Dezimale, null->"", fehlende Felder->Default,
  AssignedAccountIds-Array, Category-Default, Nicht-Array->leer.

Refactor:
- Mongo-Export-Parsing aus ConfigMigrator in testbare Klasse
  PolyTrader.Modules.CopyTrading.ConfigImport.MongoExportParser ausgelagert
  (ParseAccounts -> Account+Settings, ParseTraders). ConfigMigrator nutzt sie;
  --migrate-json end-to-end verifiziert (3/3/32).
- PolyTrader.App.csproj: tests/** vom Default-Glob ausgeschlossen (App zog sonst
  die Testdateien mit rein -> doppelte AssemblyInfo/Xunit-Fehler).

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

tests/PolyTrader.Tests/MarketRepositoryTests.cs

@@ -0,0 +1,46 @@
+using System.Linq;
+using PolyTrader.Core.Persistence.Ef;
+using PolyTrader.Tests.TestSupport;
+using PolyTraderSharp.Models;
+using Xunit;
+
+namespace PolyTrader.Tests
+{
+    public class MarketRepositoryTests
+    {
+        private static EfMarketRepository NewRepo() =>
+            new(new InMemoryContextFactory<CoreDbContext>(o => new CoreDbContext(o)));
+
+        [Fact]
+        public void GetActive_returns_only_non_closed_markets()
+        {
+            var repo = NewRepo();
+            repo.Upsert(new MarketData { Id = "m1", Closed = false });
+            repo.Upsert(new MarketData { Id = "m2", Closed = true });
+
+            var active = repo.GetActive();
+            Assert.Single(active);
+            Assert.Equal("m1", active[0].Id);
+        }
+
+        [Fact]
+        public void Upsert_updates_existing_market()
+        {
+            var repo = NewRepo();
+            repo.Upsert(new MarketData { Id = "m1", Question = "old" });
+            repo.Upsert(new MarketData { Id = "m1", Question = "new" });
+
+            Assert.Equal("new", repo.GetById("m1")!.Question);
+        }
+
+        [Fact]
+        public void FindByTokenId_matches_within_clob_token_ids()
+        {
+            var repo = NewRepo();
+            repo.Upsert(new MarketData { Id = "m1", ClobTokenIds = "[\"abc\",\"def\"]" });
+
+            Assert.Equal("m1", repo.FindByTokenId("def")!.Id);
+            Assert.Null(repo.FindByTokenId("zzz"));
+        }
+    }
+}