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/ScriptConfiguration.cs

@@ -0,0 +1,28 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+using ScadaLink.Commons.Entities.Scripts;
+
+namespace ScadaLink.ConfigurationDatabase.Configurations;
+
+public class SharedScriptConfiguration : IEntityTypeConfiguration<SharedScript>
+{
+    public void Configure(EntityTypeBuilder<SharedScript> builder)
+    {
+        builder.HasKey(s => s.Id);
+
+        builder.Property(s => s.Name)
+            .IsRequired()
+            .HasMaxLength(200);
+
+        builder.Property(s => s.Code)
+            .IsRequired();
+
+        builder.Property(s => s.ParameterDefinitions)
+            .HasMaxLength(4000);
+
+        builder.Property(s => s.ReturnDefinition)
+            .HasMaxLength(4000);
+
+        builder.HasIndex(s => s.Name).IsUnique();
+    }
+}