docs: backfill XML documentation across 756 files

Adds <summary>, <param>, <typeparam>, and <inheritdoc/> tags to public
members surfaced by commentchecker — resolves 5,847 of 5,869 issues
(99.6%) across three /fixdocs passes.

tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/OpcUa/ServiceLevelEndToEndTests.cs

@@ -24,6 +24,7 @@ public sealed class ServiceLevelEndToEndTests : RuntimeActorTestBase
 {
     private static CancellationToken Ct => CancellationToken.None;
 
+    /// <summary>Verifies that the primary cluster leader sets Server ServiceLevel to 240.</summary>
     [Fact]
     public async Task Primary_leader_drives_Server_ServiceLevel_to_240()
     {
@@ -63,6 +64,7 @@ public sealed class ServiceLevelEndToEndTests : RuntimeActorTestBase
         }
     }
 
+    /// <summary>Verifies that the secondary node sets Server ServiceLevel to 100.</summary>
     [Fact]
     public async Task Secondary_drives_Server_ServiceLevel_to_100()
     {