Phase 2 WP-1–13+23: Template Engine CRUD, composition, overrides, locking, collision detection, acyclicity

- WP-23: ITemplateEngineRepository full EF Core implementation
- WP-1: Template CRUD with deletion constraints (instances, children, compositions)
- WP-2–4: Attribute, alarm, script definitions with lock flags and override granularity
- WP-5: Shared script CRUD with syntax validation
- WP-6–7: Composition with recursive nesting and canonical naming
- WP-8–11: Override granularity, locking rules, inheritance/composition scope
- WP-12: Naming collision detection on canonical names (recursive)
- WP-13: Graph acyclicity (inheritance + composition cycles)
Core services: TemplateService, SharedScriptService, TemplateResolver,
LockEnforcer, CollisionDetector, CycleDetector. 358 tests pass.

src/ScadaLink.Commons/Interfaces/Repositories/ISiteRepository.cs

@@ -0,0 +1,35 @@
+using ScadaLink.Commons.Entities.Instances;
+using ScadaLink.Commons.Entities.Sites;
+
+namespace ScadaLink.Commons.Interfaces.Repositories;
+
+/// <summary>
+/// Repository interface for site and data connection management.
+/// </summary>
+public interface ISiteRepository
+{
+    // Sites
+    Task<Site?> GetSiteByIdAsync(int id, CancellationToken cancellationToken = default);
+    Task<Site?> GetSiteByIdentifierAsync(string siteIdentifier, CancellationToken cancellationToken = default);
+    Task<IReadOnlyList<Site>> GetAllSitesAsync(CancellationToken cancellationToken = default);
+    Task AddSiteAsync(Site site, CancellationToken cancellationToken = default);
+    Task UpdateSiteAsync(Site site, CancellationToken cancellationToken = default);
+    Task DeleteSiteAsync(int id, CancellationToken cancellationToken = default);
+
+    // Data Connections
+    Task<DataConnection?> GetDataConnectionByIdAsync(int id, CancellationToken cancellationToken = default);
+    Task<IReadOnlyList<DataConnection>> GetDataConnectionsBySiteIdAsync(int siteId, CancellationToken cancellationToken = default);
+    Task AddDataConnectionAsync(DataConnection connection, CancellationToken cancellationToken = default);
+    Task UpdateDataConnectionAsync(DataConnection connection, CancellationToken cancellationToken = default);
+    Task DeleteDataConnectionAsync(int id, CancellationToken cancellationToken = default);
+
+    // Site-Connection Assignments
+    Task<SiteDataConnectionAssignment?> GetSiteDataConnectionAssignmentAsync(int siteId, int dataConnectionId, CancellationToken cancellationToken = default);
+    Task AddSiteDataConnectionAssignmentAsync(SiteDataConnectionAssignment assignment, CancellationToken cancellationToken = default);
+    Task DeleteSiteDataConnectionAssignmentAsync(int id, CancellationToken cancellationToken = default);
+
+    // Instances (for deletion constraint checks)
+    Task<IReadOnlyList<Instance>> GetInstancesBySiteIdAsync(int siteId, CancellationToken cancellationToken = default);
+
+    Task<int> SaveChangesAsync(CancellationToken cancellationToken = default);
+}