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.AdminUI.Tests/_PlaceholderTests.cs

@@ -5,6 +5,7 @@ namespace ZB.MOM.WW.OtOpcUa.AdminUI.Tests;
 
 public sealed class _PlaceholderTests
 {
+    /// <summary>Verifies the project compiles and the test runner can discover test methods.</summary>
     [Fact]
     public void ProjectCompilesAndTestRunnerDiscoversIt() => 1.ShouldBe(1);
 }