docs: complete XML-doc coverage and strip internal tracking IDs from code comments

Resolve all CommentChecker findings across the gateway server, worker, tests,
and .NET client (314 -> 0 real issues): add missing <returns>/<summary>/<param>
on public and test members, convert Stream/interface overrides to <inheritdoc/>,
and remove internal task/issue tracking IDs (SEC-*, IPC-*, WRK-*, GWC-*, TST-*,
Client.Dotnet-*) from shipped code documentation while preserving the design
rationale prose. Shipped comments should not carry internal bookkeeping, and
complete XML docs keep the analyzer/TreatWarningsAsErrors gate and generated API
docs clean. The 6 remaining flags are heuristic false positives (MD5, UTC-4,
capacity-1, near-1601) left intact so real documentation is not corrupted.

Claude-Session: https://claude.ai/code/session_01DMXXvNuPekkkrTEyPNxEkW

src/ZB.MOM.WW.MxGateway.Server/Security/Authentication/CachingApiKeyVerifier.cs

@@ -30,7 +30,7 @@ public interface IApiKeyCacheInvalidator
 /// <para>
 /// Only successful verifications are cached. Failures and unparseable headers always fall through
 /// to the inner verifier — caching a failure risks pinning a transiently-wrong negative, and the
-/// SEC-11 per-peer failure counter (not this cache) is what bounds brute-force cost.
+/// per-peer failure counter (not this cache) is what bounds brute-force cost.
 /// </para>
 /// <para>
 /// The cache key is the hex SHA-256 of the presented token (which embeds both the key id and the
@@ -71,7 +71,11 @@ public sealed class CachingApiKeyVerifier : IApiKeyVerifier, IApiKeyCacheInvalid
     {
     }
 
-    // Test/explicit-TTL seam.
+    /// <summary>Initializes a new instance of the <see cref="CachingApiKeyVerifier"/> class with an explicit TTL.</summary>
+    /// <param name="inner">The wrapped verifier (the library verifier) reached on a cache miss.</param>
+    /// <param name="cache">The shared memory cache.</param>
+    /// <param name="ttl">The verification-cache TTL; a zero or negative value disables caching.</param>
+    /// <remarks>Test/explicit-TTL seam.</remarks>
     internal CachingApiKeyVerifier(IApiKeyVerifier inner, IMemoryCache cache, TimeSpan ttl)
     {
         ArgumentNullException.ThrowIfNull(inner);
@@ -81,7 +85,14 @@ public sealed class CachingApiKeyVerifier : IApiKeyVerifier, IApiKeyCacheInvalid
         _ttl = ttl;
     }
 
-    /// <inheritdoc />
+    /// <summary>
+    /// Verifies the given authorization header, returning a cached successful result when one is
+    /// still within TTL, or falling through to the inner verifier on a cache miss or non-cacheable
+    /// header.
+    /// </summary>
+    /// <param name="authorizationHeader">The raw <c>Authorization</c> header value to verify.</param>
+    /// <param name="ct">Token to cancel the asynchronous operation.</param>
+    /// <returns>The verification result, cached or freshly computed.</returns>
     public async Task<ApiKeyVerification> VerifyAsync(string authorizationHeader, CancellationToken ct)
     {
         if (_ttl <= TimeSpan.Zero || !TryComputeCacheKey(authorizationHeader, out string cacheKey))