fix(client-shared): resolve Low code-review findings (Client.Shared-003,004,009,010,011)

- Client.Shared-003: DefaultSessionAdapter.WriteValueAsync / CallMethodAsync
  guard against null/empty Results and throw ServiceResultException with
  the response's ServiceResult code instead of indexing into a missing
  list.
- Client.Shared-004: DefaultSessionAdapter.CloseAsync / HistoryReadRawAsync
  / HistoryReadAggregateAsync use the Session.*Async overloads and honour
  the caller's CancellationToken.
- Client.Shared-009: AcknowledgeAlarmAsync returns the underlying
  ServiceResultException.StatusCode on failure instead of always Good;
  IOpcUaClientService doc updated to describe the new contract.
- Client.Shared-010: ConnectionSettings.CertificateStorePath defaults to
  empty; DefaultApplicationConfigurationFactory resolves the canonical
  PKI path lazily, so per-failover ConnectionSettings copies don't hit
  the filesystem.
- Client.Shared-011: added the alarm-fallback regression test, extracted
  EndpointSelector as a pure static, and added EndpointSelectorTests
  covering security-mode match, Basic256Sha256 preference, fallback,
  diagnostics, hostname rewrite, and null/empty guards.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/Client/ZB.MOM.WW.OtOpcUa.Client.Shared/OpcUaClientService.cs

@@ -353,11 +353,24 @@ public sealed class OpcUaClientService : IOpcUaClientService
             : NodeId.Parse(conditionNodeId + ".Condition");
         var acknowledgeMethodId = MethodIds.AcknowledgeableConditionType_Acknowledge;
 
-        await _session!.CallMethodAsync(
-            conditionObjId,
-            acknowledgeMethodId,
-            [eventId, new LocalizedText(comment)],
-            ct);
+        // CallMethodAsync throws ServiceResultException on a bad call result;
+        // surface that as the returned StatusCode so callers using the documented
+        // `Task<StatusCode>` contract (e.g. `if (StatusCode.IsBad(result))`) see
+        // the failure instead of an uncaught exception they did not anticipate.
+        try
+        {
+            await _session!.CallMethodAsync(
+                conditionObjId,
+                acknowledgeMethodId,
+                [eventId, new LocalizedText(comment)],
+                ct);
+        }
+        catch (ServiceResultException ex)
+        {
+            Logger.Warning(ex, "Failed to acknowledge alarm on {ConditionId} (status {Status})",
+                conditionNodeId, ex.StatusCode);
+            return ex.StatusCode;
+        }
 
         Logger.Debug("Acknowledged alarm on {ConditionId}", conditionNodeId);
         return StatusCodes.Good;