Phase 7: Mapping-Randfälle + Parser-/Repo-Randfälle (78 Tests)

- DbContextModelTests: feinkörnige Modell-Invarianten - Dezimal-Präzision (18,6)
  auf Geldfeldern (Core + Settings), MaxLength auf Strings, manuell gesetzte Keys
  (ValueGeneratedNever), AssignedAccountIds hat Value-Converter + text-Spalte,
  MarketData JSON-Spalten = text, Indizes (TradeRecord.ClosedAt,
  MasterTraderHistory TraderId/ClosedAt).
  (GetColumnType() wirft unter InMemory -> Spaltentyp via Relational:ColumnType-
  Annotation ausgelesen.)
- MongoExportParserTests erweitert: numerische statt String-Dezimale, unbekannte
  Felder ignoriert, mehrere Dokumente in Reihenfolge, AssignedAccountIds als
  String-Zahlen, IsActive-Default.
- RepositoryEdgeCaseTests: GetAll leer != null, Update-Alias, Factory-Isolation,
  History-Exists/GetByTraderSince inklusive an den Grenzen.

Alle 78 gruen. (Copytrading-Service-Logik bewusst noch nicht getestet - wird
parallel ueberarbeitet.)

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

tests/PolyTrader.Tests/MongoExportParserTests.cs

@@ -116,5 +116,51 @@ namespace PolyTrader.Tests
             Assert.Empty(MongoExportParser.ParseAccounts("[]"));
             Assert.Empty(MongoExportParser.ParseTraders("[]"));
         }
+
+        [Fact]
+        public void ParseAccounts_accepts_numeric_decimals_not_only_strings()
+        {
+            const string json = """[{ "_id": 1, "TotalBalance": 12.5, "PerMarketLimit": 3 }]""";
+
+            var imp = Assert.Single(MongoExportParser.ParseAccounts(json));
+            Assert.Equal(12.5m, imp.Account.TotalBalance);
+            Assert.Equal(3m, imp.Settings.PerMarketLimit);
+        }
+
+        [Fact]
+        public void ParseAccounts_ignores_unknown_extra_fields()
+        {
+            const string json = """[{ "_id": 1, "Name": "X", "SomethingUnknown": {"a":1}, "Extra": [1,2,3] }]""";
+
+            var imp = Assert.Single(MongoExportParser.ParseAccounts(json));
+            Assert.Equal("X", imp.Account.Name);
+        }
+
+        [Fact]
+        public void ParseAccounts_reads_multiple_documents_in_order()
+        {
+            const string json = """[{ "_id": 1 }, { "_id": 2 }, { "_id": 3 }]""";
+
+            var ids = MongoExportParser.ParseAccounts(json).Select(x => x.Account.AccountId).ToArray();
+            Assert.Equal(new[] { 1, 2, 3 }, ids);
+        }
+
+        [Fact]
+        public void ParseTraders_accepts_assigned_account_ids_as_string_numbers()
+        {
+            const string json = """[{ "_id": 9, "AssignedAccountIds": ["1", "3"] }]""";
+
+            var t = Assert.Single(MongoExportParser.ParseTraders(json));
+            Assert.Equal(new HashSet<int> { 1, 3 }, t.AssignedAccountIds);
+        }
+
+        [Fact]
+        public void ParseTraders_missing_isactive_defaults_true()
+        {
+            const string json = """[{ "_id": 9 }]""";
+
+            var t = Assert.Single(MongoExportParser.ParseTraders(json));
+            Assert.True(t.IsActive);
+        }
     }
 }