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.Runtime.Tests/OpcUa/ServiceLevelEndToEndTests.cs

@@ -25,6 +25,7 @@ public sealed class ServiceLevelEndToEndTests : RuntimeActorTestBase
     private static CancellationToken Ct => CancellationToken.None;
 
     /// <summary>Verifies that the primary cluster leader sets Server ServiceLevel to 240.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task Primary_leader_drives_Server_ServiceLevel_to_240()
     {
@@ -65,6 +66,7 @@ public sealed class ServiceLevelEndToEndTests : RuntimeActorTestBase
     }
 
     /// <summary>Verifies that the secondary node sets Server ServiceLevel to 100.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task Secondary_drives_Server_ServiceLevel_to_100()
     {