docs: complete XML doc comments via fixdocs (2757 to 131 findings)

Add missing <returns>/<param>/<summary>/<typeparam> tags and clean up
misused inheritdoc across 481 files so the documented API surface is
complete. Documentation-only (zero code lines changed). The 131 remaining
findings are inheritdoc-style warnings deliberately left to preserve
hand-written implementation rationale (plan-decision notes, race-condition
explanations).

tests/Client/ZB.MOM.WW.OtOpcUa.Client.UI.Tests/AlarmsViewModelTests.cs

@@ -47,6 +47,7 @@ public class AlarmsViewModelTests
     }
 
     /// <summary>Verifies that SubscribeCommand sets IsSubscribed flag.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task SubscribeCommand_SetsIsSubscribed()
     {
@@ -68,6 +69,7 @@ public class AlarmsViewModelTests
     }
 
     /// <summary>Verifies that UnsubscribeCommand clears IsSubscribed flag.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task UnsubscribeCommand_ClearsIsSubscribed()
     {
@@ -81,6 +83,7 @@ public class AlarmsViewModelTests
     }
 
     /// <summary>Verifies that RefreshCommand calls the service.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RefreshCommand_CallsService()
     {
@@ -156,6 +159,7 @@ public class AlarmsViewModelTests
     /// Regression test for Client.UI-006 — when SubscribeAlarmsAsync throws, the failure must be
     /// surfaced to the operator via the view model's StatusMessage rather than silently swallowed.
     /// </summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task Subscribe_OnFailure_SurfacesStatusMessage()
     {