fix(alarms): surface composed-member attributes across flatten/validate/UI

Three layers were each blind to nested composition in different ways:

- FlatteningPipeline only loaded compositions for templates in the parent's
  inheritance chain, so depth-2 composed attributes (e.g.
  Pump.AlarmSensor.SensorReading) never materialized. Walk composed chains
  breadth-first so the flattener's nested step has the data it needs.

- InstanceConfigure's alarm trigger picker was fed only direct, non-locked
  attributes, hiding inherited and composed-member paths. Feed it the full
  flattened attribute list via FlatteningPipeline.

- ValidationService.ExtractAttributeNameFromTriggerConfig only recognized
  "attributeName", silently passing alarms still using the legacy
  "attribute" key. Accept both keys, matching FlatteningService,
  AlarmActor, and AlarmTriggerConfigCodec.

src/ScadaLink.TemplateEngine/Validation/ValidationService.cs

@@ -220,11 +220,16 @@ public class ValidationService
 
     internal static string? ExtractAttributeNameFromTriggerConfig(string triggerConfigJson)
     {
+        // Accept both keys to stay consistent with FlatteningService.PrefixTriggerAttribute,
+        // AlarmActor.ParseEvalConfig and AlarmTriggerConfigCodec. Old data may still use
+        // "attribute"; the UI codec writes the canonical "attributeName".
         try
         {
             using var doc = JsonDocument.Parse(triggerConfigJson);
             if (doc.RootElement.TryGetProperty("attributeName", out var prop))
                 return prop.GetString();
+            if (doc.RootElement.TryGetProperty("attribute", out var legacyProp))
+                return legacyProp.GetString();
         }
         catch (JsonException)
         {