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/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/SdkAddressSpaceSinkTests.cs

@@ -20,6 +20,7 @@ public sealed class SdkAddressSpaceSinkTests : IDisposable
         $"otopcua-sink-{Guid.NewGuid():N}");
 
     /// <summary>Verifies that WriteValue creates and updates variables in the OPC UA node manager.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task WriteValue_creates_and_updates_variable_in_node_manager()
     {
@@ -36,6 +37,7 @@ public sealed class SdkAddressSpaceSinkTests : IDisposable
     }
 
     /// <summary>Verifies that WriteAlarmState creates a dedicated node distinct from value writes.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task WriteAlarmState_creates_dedicated_node_distinct_from_value_writes()
     {
@@ -51,6 +53,7 @@ public sealed class SdkAddressSpaceSinkTests : IDisposable
     }
 
     /// <summary>Verifies that RebuildAddressSpace clears all registered variables.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task RebuildAddressSpace_clears_all_registered_variables()
     {
@@ -73,6 +76,7 @@ public sealed class SdkAddressSpaceSinkTests : IDisposable
     }
 
     /// <summary>Verifies that NullOpcUaAddressSpaceSink does not crash on any call.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task NullOpcUaAddressSpaceSink_does_not_crash_on_any_call()
     {