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/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/OpcUaClientAlarmTests.cs

@@ -33,6 +33,7 @@ public sealed class OpcUaClientAlarmTests
     }
 
     /// <summary>Verifies that SubscribeAlarmsAsync without initialize throws InvalidOperationException.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task SubscribeAlarmsAsync_without_initialize_throws_InvalidOperationException()
     {
@@ -42,6 +43,7 @@ public sealed class OpcUaClientAlarmTests
     }
 
     /// <summary>Verifies that UnsubscribeAlarmsAsync with unknown handle is noop.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task UnsubscribeAlarmsAsync_with_unknown_handle_is_noop()
     {
@@ -51,6 +53,7 @@ public sealed class OpcUaClientAlarmTests
     }
 
     /// <summary>Verifies that AcknowledgeAsync without initialize throws InvalidOperationException.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task AcknowledgeAsync_without_initialize_throws_InvalidOperationException()
     {
@@ -62,6 +65,7 @@ public sealed class OpcUaClientAlarmTests
     }
 
     /// <summary>Verifies that AcknowledgeAsync with empty batch is noop even without init.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task AcknowledgeAsync_with_empty_batch_is_noop_even_without_init()
     {
@@ -73,7 +77,7 @@ public sealed class OpcUaClientAlarmTests
 
     private sealed class FakeAlarmHandle : IAlarmSubscriptionHandle
     {
-        /// <summary>Gets the diagnostic identifier for this alarm handle.</summary>
+        /// <inheritdoc />
         public string DiagnosticId => "fake-alarm";
     }
 }