feat: postgres history-first 계약과 적재 경로 추가

- PostgreSQL history contract와 schema/validator를 추가했습니다.
- .NET history store, snapshot reader, repository, migration을 연결했습니다.
- history-first 운영 모델 문서와 daily signal tracking 문구를 정리했습니다.

src/dotnet/QuantEngine.Application/Services/WorkspaceService.cs

@@ -9,10 +9,12 @@ namespace QuantEngine.Application.Services
     public class WorkspaceService
     {
         private readonly IWorkspaceRepository _repository;
+        private readonly IPostgresqlHistoryStore _historyStore;
 
-        public WorkspaceService(IWorkspaceRepository repository)
+        public WorkspaceService(IWorkspaceRepository repository, IPostgresqlHistoryStore historyStore)
         {
             _repository = repository;
+            _historyStore = historyStore;
         }
 
         public Task<IEnumerable<Setting>> GetSettingsAsync() => _repository.GetSettingsAsync();
@@ -23,5 +25,8 @@ namespace QuantEngine.Application.Services
         public Task<IEnumerable<AccountSnapshot>> GetAccountSnapshotsAsync() => _repository.GetAccountSnapshotsAsync();
         public Task<bool> InsertAccountSnapshotsAsync(IEnumerable<AccountSnapshot> snapshots) => _repository.InsertAccountSnapshotsAsync(snapshots);
         public Task<bool> ClearAccountSnapshotsAsync() => _repository.ClearAccountSnapshotsAsync();
+
+        public Task<int> AppendHistoryAsync(string domain, IDictionary<string, object?> payload) => _historyStore.AppendAsync(domain, payload);
+        public Task<IReadOnlyList<IDictionary<string, object?>>> ReadHistorySnapshotAsync(string domain, int limit = 500) => _historyStore.SnapshotAsync(domain, limit);
     }
 }