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/ScadaLinkDbContext.cs

@@ -0,0 +1,71 @@
+using Microsoft.EntityFrameworkCore;
+using ScadaLink.Commons.Entities.Audit;
+using ScadaLink.Commons.Entities.Deployment;
+using ScadaLink.Commons.Entities.ExternalSystems;
+using ScadaLink.Commons.Entities.InboundApi;
+using ScadaLink.Commons.Entities.Instances;
+using ScadaLink.Commons.Entities.Notifications;
+using ScadaLink.Commons.Entities.Scripts;
+using ScadaLink.Commons.Entities.Security;
+using ScadaLink.Commons.Entities.Sites;
+using ScadaLink.Commons.Entities.Templates;
+
+namespace ScadaLink.ConfigurationDatabase;
+
+public class ScadaLinkDbContext : DbContext
+{
+    public ScadaLinkDbContext(DbContextOptions<ScadaLinkDbContext> options) : base(options)
+    {
+    }
+
+    // Templates
+    public DbSet<Template> Templates => Set<Template>();
+    public DbSet<TemplateAttribute> TemplateAttributes => Set<TemplateAttribute>();
+    public DbSet<TemplateAlarm> TemplateAlarms => Set<TemplateAlarm>();
+    public DbSet<TemplateScript> TemplateScripts => Set<TemplateScript>();
+    public DbSet<TemplateComposition> TemplateCompositions => Set<TemplateComposition>();
+
+    // Instances
+    public DbSet<Instance> Instances => Set<Instance>();
+    public DbSet<InstanceAttributeOverride> InstanceAttributeOverrides => Set<InstanceAttributeOverride>();
+    public DbSet<InstanceConnectionBinding> InstanceConnectionBindings => Set<InstanceConnectionBinding>();
+    public DbSet<Area> Areas => Set<Area>();
+
+    // Sites
+    public DbSet<Site> Sites => Set<Site>();
+    public DbSet<DataConnection> DataConnections => Set<DataConnection>();
+    public DbSet<SiteDataConnectionAssignment> SiteDataConnectionAssignments => Set<SiteDataConnectionAssignment>();
+
+    // Deployment
+    public DbSet<DeploymentRecord> DeploymentRecords => Set<DeploymentRecord>();
+    public DbSet<SystemArtifactDeploymentRecord> SystemArtifactDeploymentRecords => Set<SystemArtifactDeploymentRecord>();
+
+    // External Systems
+    public DbSet<ExternalSystemDefinition> ExternalSystemDefinitions => Set<ExternalSystemDefinition>();
+    public DbSet<ExternalSystemMethod> ExternalSystemMethods => Set<ExternalSystemMethod>();
+    public DbSet<DatabaseConnectionDefinition> DatabaseConnectionDefinitions => Set<DatabaseConnectionDefinition>();
+
+    // Notifications
+    public DbSet<NotificationList> NotificationLists => Set<NotificationList>();
+    public DbSet<NotificationRecipient> NotificationRecipients => Set<NotificationRecipient>();
+    public DbSet<SmtpConfiguration> SmtpConfigurations => Set<SmtpConfiguration>();
+
+    // Scripts
+    public DbSet<SharedScript> SharedScripts => Set<SharedScript>();
+
+    // Security
+    public DbSet<LdapGroupMapping> LdapGroupMappings => Set<LdapGroupMapping>();
+    public DbSet<SiteScopeRule> SiteScopeRules => Set<SiteScopeRule>();
+
+    // Inbound API
+    public DbSet<ApiKey> ApiKeys => Set<ApiKey>();
+    public DbSet<ApiMethod> ApiMethods => Set<ApiMethod>();
+
+    // Audit
+    public DbSet<AuditLogEntry> AuditLogEntries => Set<AuditLogEntry>();
+
+    protected override void OnModelCreating(ModelBuilder modelBuilder)
+    {
+        modelBuilder.ApplyConfigurationsFromAssembly(typeof(ScadaLinkDbContext).Assembly);
+    }
+}