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.Security.Tests/Audit/AuditActorTests.cs

@@ -76,6 +76,7 @@ public sealed class AuditActorTests
 
     private sealed class StubAccessor(string? value) : IAuditActorAccessor
     {
+        /// <inheritdoc />
         public string? CurrentActor { get; } = value;
     }
 }

tests/Server/ZB.MOM.WW.OtOpcUa.Security.Tests/Audit/HttpAuditActorAccessorTests.cs

@@ -110,6 +110,7 @@ public sealed class HttpAuditActorAccessorTests
 
     private sealed class HttpContextAccessorStub(HttpContext? context) : IHttpContextAccessor
     {
+        /// <summary>Gets or sets the HTTP context for the stub.</summary>
         public HttpContext? HttpContext { get; set; } = context;
     }
 }