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.Host.IntegrationTests/FleetDiagnosticsRoundTripTests.cs

@@ -17,6 +17,7 @@ public sealed class FleetDiagnosticsRoundTripTests
     private static CancellationToken Ct => TestContext.Current.CancellationToken;
 
     /// <summary>Verifies that get diagnostics returns a snapshot with the target node ID.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task GetDiagnostics_returns_snapshot_with_target_NodeId()
     {
@@ -41,6 +42,7 @@ public sealed class FleetDiagnosticsRoundTripTests
     }
 
     /// <summary>Verifies that get diagnostics after deploy reports the current revision.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task GetDiagnostics_after_deploy_reports_current_revision()
     {