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.ControlPlane.Tests/AuditWriterActorTests.cs

@@ -139,6 +139,7 @@ public sealed class AuditWriterActorTests : ControlPlaneActorTestBase
     /// synchronously, never throws, and routes the event onto the actor's own mailbox
     /// (<c>Self.Tell</c>) — i.e. the same buffer + dedup + flush pipeline asserted by the Tell
     /// tests above. Reaches the concrete instance via a TestActorRef.</summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task WriteAsync_is_best_effort_and_routes_onto_the_actor_mailbox()
     {
@@ -197,6 +198,8 @@ public sealed class AuditWriterActorTests : ControlPlaneActorTestBase
 
     /// <summary>Verifies the Outcome derivation table: config verbs → Success, the two
     /// authorization-rejection events → Denied.</summary>
+    /// <param name="action">The audit action string to derive the outcome from.</param>
+    /// <param name="expected">The expected audit outcome for the given action.</param>
     [Theory]
     [InlineData("DraftCreated", AuditOutcome.Success)]
     [InlineData("DraftEdited", AuditOutcome.Success)]