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/ReadWriteViewModelTests.cs

@@ -51,6 +51,7 @@ public class ReadWriteViewModelTests
     }
 
     /// <summary>Verifies that the read command updates value and status.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task ReadCommand_UpdatesValueAndStatus()
     {
@@ -91,6 +92,7 @@ public class ReadWriteViewModelTests
     }
 
     /// <summary>Verifies that the write command updates write status.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task WriteCommand_UpdatesWriteStatus()
     {
@@ -118,6 +120,7 @@ public class ReadWriteViewModelTests
     }
 
     /// <summary>Verifies that read command error sets error status.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task ReadCommand_Error_SetsErrorStatus()
     {