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/AuditConfiguration.cs

@@ -0,0 +1,40 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+using ScadaLink.Commons.Entities.Audit;
+
+namespace ScadaLink.ConfigurationDatabase.Configurations;
+
+public class AuditLogEntryConfiguration : IEntityTypeConfiguration<AuditLogEntry>
+{
+    public void Configure(EntityTypeBuilder<AuditLogEntry> builder)
+    {
+        builder.HasKey(a => a.Id);
+
+        builder.Property(a => a.User)
+            .IsRequired()
+            .HasMaxLength(200);
+
+        builder.Property(a => a.Action)
+            .IsRequired()
+            .HasMaxLength(100);
+
+        builder.Property(a => a.EntityType)
+            .IsRequired()
+            .HasMaxLength(200);
+
+        builder.Property(a => a.EntityId)
+            .IsRequired()
+            .HasMaxLength(200);
+
+        builder.Property(a => a.EntityName)
+            .IsRequired()
+            .HasMaxLength(200);
+
+        // Indexes for common query patterns
+        builder.HasIndex(a => a.Timestamp);
+        builder.HasIndex(a => a.User);
+        builder.HasIndex(a => a.EntityType);
+        builder.HasIndex(a => a.EntityId);
+        builder.HasIndex(a => a.Action);
+    }
+}