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/OpcUaApplicationHostSecurityTests.cs

@@ -91,6 +91,7 @@ public sealed class OpcUaApplicationHostSecurityTests : IDisposable
     /// <summary>
     /// Verifies that StartAsync populates ServerConfiguration with all enabled security profiles.
     /// </summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task StartAsync_populates_ServerConfiguration_with_all_enabled_profiles()
     {
@@ -129,6 +130,7 @@ public sealed class OpcUaApplicationHostSecurityTests : IDisposable
     /// <summary>
     /// Verifies that StartAsync with only SignAndEncrypt omits the None endpoint.
     /// </summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     [Fact]
     public async Task StartAsync_with_only_signandencrypt_omits_None_endpoint()
     {