fix(deploy): a node with a ConfigDb records its degraded apply on its own NodeDeploymentState row (#601 review)

The apply writes the node's row Applied/null before the address-space outcome
is known; central adds the reason only when it ACCEPTS the ack, so a discarded
(stale/timed-out) ack left a fused node's row reading clean. The prefix moves
to ApplyAck.DegradedReasonPrefix so both writers spell the row identically.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

src/Core/ZB.MOM.WW.OtOpcUa.Commons/Messages/Deploy/ApplyAck.cs

@@ -27,4 +27,12 @@ public sealed record ApplyAck(
     string? FailureReason,
     CorrelationId CorrelationId,
     bool Degraded = false,
-    string? DegradedReason = null);
+    string? DegradedReason = null)
+{
+    /// <summary>
+    ///     Gitea #601 — prefix of <c>NodeDeploymentState.FailureReason</c> on an <b>Applied</b> row whose
+    ///     address-space apply was degraded. Shared by central (which writes it from the ack) and a node with
+    ///     a ConfigDb (which writes its own row), so both spell the row identically.
+    /// </summary>
+    public const string DegradedReasonPrefix = "Applied degraded: ";
+}