Phase 1 WP-1: EF Core DbContext with Fluent API mappings for all 26 entities

ScadaLinkDbContext with 10 configuration classes (Fluent API only), initial
migration creating 25 tables, environment-aware migration helper (auto-apply
dev, validate-only prod), DesignTimeDbContextFactory, optimistic concurrency
on DeploymentRecord. 20 tests verify schema, CRUD, relationships, cascades.

src/ScadaLink.ConfigurationDatabase/Configurations/DeploymentConfiguration.cs

@@ -0,0 +1,63 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+using ScadaLink.Commons.Entities.Deployment;
+using ScadaLink.Commons.Entities.Instances;
+
+namespace ScadaLink.ConfigurationDatabase.Configurations;
+
+public class DeploymentRecordConfiguration : IEntityTypeConfiguration<DeploymentRecord>
+{
+    public void Configure(EntityTypeBuilder<DeploymentRecord> builder)
+    {
+        builder.HasKey(d => d.Id);
+
+        builder.Property(d => d.DeploymentId)
+            .IsRequired()
+            .HasMaxLength(100);
+
+        builder.Property(d => d.RevisionHash)
+            .HasMaxLength(100);
+
+        builder.Property(d => d.DeployedBy)
+            .IsRequired()
+            .HasMaxLength(200);
+
+        builder.Property(d => d.Status)
+            .HasConversion<string>()
+            .HasMaxLength(50);
+
+        builder.HasOne<Instance>()
+            .WithMany()
+            .HasForeignKey(d => d.InstanceId)
+            .OnDelete(DeleteBehavior.Restrict);
+
+        // Optimistic concurrency on deployment status records
+        builder.Property<byte[]>("RowVersion")
+            .IsRowVersion();
+
+        builder.HasIndex(d => d.DeploymentId).IsUnique();
+        builder.HasIndex(d => d.InstanceId);
+        builder.HasIndex(d => d.DeployedAt);
+    }
+}
+
+public class SystemArtifactDeploymentRecordConfiguration : IEntityTypeConfiguration<SystemArtifactDeploymentRecord>
+{
+    public void Configure(EntityTypeBuilder<SystemArtifactDeploymentRecord> builder)
+    {
+        builder.HasKey(d => d.Id);
+
+        builder.Property(d => d.ArtifactType)
+            .IsRequired()
+            .HasMaxLength(100);
+
+        builder.Property(d => d.DeployedBy)
+            .IsRequired()
+            .HasMaxLength(200);
+
+        builder.Property(d => d.PerSiteStatus)
+            .HasMaxLength(4000);
+
+        builder.HasIndex(d => d.DeployedAt);
+    }
+}