fix(security): enforce template locks on native alarm source overrides at flatten and management-command level

Add IsLocked to ResolvedNativeAlarmSource; FlatteningService skips overrides on a
locked source (mirrors attribute/alarm lock rules); ManagementActor SetInstanceNativeAlarmSourceOverride
flattens the instance and rejects an override on a locked source (and rejects a
canonical name that does not resolve, preventing dangling overrides).

Claude-Session: https://claude.ai/code/session_01MtdgwpEeCUn6cUA5f1LMPj

src/ZB.MOM.WW.ScadaBridge.Commons/Types/Flattening/FlattenedConfiguration.cs

@@ -146,6 +146,12 @@ public sealed record ResolvedNativeAlarmSource
     public string? ConditionFilter { get; init; }
     /// <summary>Gets the source of this binding: "Template", "Inherited", "Composed", or "Override".</summary>
     public string Source { get; init; } = "Template";
+    /// <summary>
+    /// Gets whether this native alarm source is locked at the template level. A locked
+    /// source cannot be repointed by an instance override — mirrors the attribute/alarm
+    /// lock semantics.
+    /// </summary>
+    public bool IsLocked { get; init; }
 }
 
 /// <summary>