Phase 0 WP-0.2–0.9: Implement Commons (types, entities, interfaces, messages, protocol, tests)

- WP-0.2: Namespace/folder skeleton (26 directories)
- WP-0.3: Shared data types (6 enums, RetryPolicy, Result<T>)
- WP-0.4: 24 domain entity POCOs across 10 domain areas
- WP-0.5: 7 repository interfaces with full CRUD signatures
- WP-0.6: IAuditService cross-cutting interface
- WP-0.7: 26 message contract records across 8 concern areas
- WP-0.8: IDataConnection protocol abstraction with batch ops
- WP-0.9: 8 architectural constraint enforcement tests
All 40 tests pass, zero warnings.

src/ScadaLink.Commons/Entities/Audit/AuditLogEntry.cs

@@ -0,0 +1,22 @@
+namespace ScadaLink.Commons.Entities.Audit;
+
+public class AuditLogEntry
+{
+    public int Id { get; set; }
+    public string User { get; set; }
+    public string Action { get; set; }
+    public string EntityType { get; set; }
+    public string EntityId { get; set; }
+    public string EntityName { get; set; }
+    public string? AfterStateJson { get; set; }
+    public DateTimeOffset Timestamp { get; set; }
+
+    public AuditLogEntry(string user, string action, string entityType, string entityId, string entityName)
+    {
+        User = user ?? throw new ArgumentNullException(nameof(user));
+        Action = action ?? throw new ArgumentNullException(nameof(action));
+        EntityType = entityType ?? throw new ArgumentNullException(nameof(entityType));
+        EntityId = entityId ?? throw new ArgumentNullException(nameof(entityId));
+        EntityName = entityName ?? throw new ArgumentNullException(nameof(entityName));
+    }
+}