feat(infrastructure): implement ISQLExecutor with EF6/EF Core support

- Move ISQLExecutor interface from Application to Domain layer
  - Follow Clean Architecture: Infrastructure references Domain, not Application
  - Namespace: ECMJobRunner.Domain.Interfaces
- Implement SQLExecutor service with conditional compilation
  - EF6 (net480): Database.SqlQuery<T>()
  - EF Core (net8.0): Database.SqlQueryRaw<T>()
- Register ISQLExecutor in DI (AddInfrastructure, AddInfrastructureInMemory)
  - Scoped lifetime (aligns with DbContext)

ECMJobRunner.Domain/Interfaces/ISQLExecutor.cs

@@ -0,0 +1,20 @@
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace ECMJobRunner.Domain.Interfaces
+{
+    /// <summary>
+    /// Interface for executing SQL queries and mapping results to DTOs
+    /// </summary>
+    public interface ISQLExecutor
+    {
+        /// <summary>
+        /// Executes a SQL query and maps the result to the specified type
+        /// </summary>
+        /// <typeparam name="TResult">The type to map the query result to</typeparam>
+        /// <param name="sql">The SQL query to execute</param>
+        /// <param name="cancellationToken">Cancellation token</param>
+        /// <returns>The mapped result or null if no result</returns>
+        Task<TResult?> ExecuteQueryAsync<TResult>(string sql, CancellationToken cancellationToken = default);
+    }
+}