Add JobRunnerDbContext with multi-framework support

Introduce `JobRunnerDbContext` to support both EF6 (.NET 4.8)
and EF Core (.NET 8) using conditional compilation. Add `DbSet`
properties for `CfgProfiles`, `ProfileSqlJobs`, and
`ProfileHistories`. Provide constructors for both frameworks
to handle connection strings or options. Ensure compatibility
with multiple runtime environments.

ECMJobRunner.Infrastructure/Data/JobRunnerDbContext.cs

@@ -0,0 +1,53 @@
+#if NET48
+using System.Data.Entity;
+#else
+using Microsoft.EntityFrameworkCore;
+#endif
+using ECMJobRunner.Domain.Entities;
+
+namespace ECMJobRunner.Infrastructure.Data
+{
+    /// <summary>
+    /// Entity Framework DbContext for ECM Job Runner
+    /// </summary>
+    public class JobRunnerDbContext : DbContext
+    {
+        /// <summary>
+        /// Profile entities
+        /// </summary>
+        public DbSet<CfgProfile> CfgProfiles { get; set; } = null!;
+
+        /// <summary>
+        /// ProfileSqlJob entities
+        /// </summary>
+        public DbSet<ProfileSqlJob> ProfileSqlJobs { get; set; } = null!;
+
+        /// <summary>
+        /// ProfileHistory entities
+        /// </summary>
+        public DbSet<ProfileHistory> ProfileHistories { get; set; } = null!;
+
+#if NET48
+        /// <summary>
+        /// Default constructor for Entity Framework 6 (.NET Framework 4.8)
+        /// </summary>
+        public JobRunnerDbContext() : base("name=JobRunnerConnection")
+        {
+        }
+
+        /// <summary>
+        /// Constructor with connection string for Entity Framework 6
+        /// </summary>
+        public JobRunnerDbContext(string connectionString) : base(connectionString)
+        {
+        }
+#else
+        /// <summary>
+        /// Constructor for Entity Framework Core (.NET 8)
+        /// </summary>
+        public JobRunnerDbContext(DbContextOptions<JobRunnerDbContext> options) : base(options)
+        {
+        }
+#endif
+    }
+}