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/MigrationHelper.cs

@@ -0,0 +1,41 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging;
+
+namespace ScadaLink.ConfigurationDatabase;
+
+/// <summary>
+/// Provides environment-aware migration behavior for the ScadaLink configuration database.
+/// </summary>
+public static class MigrationHelper
+{
+    /// <summary>
+    /// Applies pending migrations (development mode) or validates schema version (production mode).
+    /// </summary>
+    /// <param name="dbContext">The database context to migrate or validate.</param>
+    /// <param name="isDevelopment">When true, auto-applies migrations. When false, validates schema version matches.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    public static async Task ApplyOrValidateMigrationsAsync(
+        ScadaLinkDbContext dbContext,
+        bool isDevelopment,
+        CancellationToken cancellationToken = default)
+    {
+        if (isDevelopment)
+        {
+            await dbContext.Database.MigrateAsync(cancellationToken);
+        }
+        else
+        {
+            var pendingMigrations = await dbContext.Database.GetPendingMigrationsAsync(cancellationToken);
+            var pending = pendingMigrations.ToList();
+            if (pending.Count > 0)
+            {
+                throw new InvalidOperationException(
+                    $"Database schema is out of date. {pending.Count} pending migration(s): {string.Join(", ", pending)}. " +
+                    "Apply migrations using 'dotnet ef database update' or the generated SQL scripts before starting in production mode.");
+            }
+        }
+    }
+}