feat: add DEX job common infrastructure

Add foundational types for DEX job execution:

Constants:
- ErrorAction enum (Ignore, Stop) for error handling strategy

DTOs:
- CheckQueryResult: check query execution result with ReturnValue
- MainQueryResult: main query execution result with ReturnValue

Interfaces:
- ISQLExecutor: abstraction for SQL query execution and DTO mapping

All types include comprehensive XML documentation

ECMJobRunner.Application/Common/Constants/ErrorAction.cs

@@ -0,0 +1,18 @@
+namespace ECMJobRunner.Application.Common.Constants
+{
+    /// <summary>
+    /// Defines actions to take when an error occurs during job execution
+    /// </summary>
+    public enum ErrorAction
+    {
+        /// <summary>
+        /// Ignore the error and continue execution
+        /// </summary>
+        Ignore,
+
+        /// <summary>
+        /// Stop execution and throw an exception
+        /// </summary>
+        Stop,
+    }
+}

ECMJobRunner.Application/Common/Dtos/CheckQueryResult.cs

@@ -0,0 +1,16 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace ECMJobRunner.Application.Common.Dtos
+{
+    /// <summary>
+    /// Result of a check query execution
+    /// </summary>
+    public class CheckQueryResult
+    {
+        /// <summary>
+        /// Return value from the check query (expected: > 0 for success)
+        /// </summary>
+        [Column("Return Value")]
+        public int? ReturnValue { get; set; }
+    }
+}

ECMJobRunner.Application/Common/Dtos/MainQueryResult.cs

@@ -0,0 +1,16 @@
+using System.ComponentModel.DataAnnotations.Schema;
+
+namespace ECMJobRunner.Application.Common.Dtos
+{
+    /// <summary>
+    /// Result of a main query execution
+    /// </summary>
+    public class MainQueryResult
+    {
+        /// <summary>
+        /// Return value from the main query (expected: null for success)
+        /// </summary>
+        [Column("Return Value")]
+        public int? ReturnValue { get; set; }
+    }
+}

ECMJobRunner.Application/Common/Interfaces/ISQLExecutor.cs

@@ -0,0 +1,20 @@
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace ECMJobRunner.Application.Common.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);
+    }
+}