docs(src): add missing XML docs and strip tracking-ID comments

Sweep of 203 source files resolving CommentChecker findings: add
<summary>/<param>/<returns>/<inheritdoc> where missing, and remove
resolved task/issue tracking markers (Tests-NNN, Worker-NNN, Server-NNN,
Task N) from code comments. Comment/doc-only — no logic changes.
Server+Tests build clean under TreatWarningsAsErrors.

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

@@ -26,6 +26,7 @@ public sealed class ApiKeyAdminCliRunner(ApiKeyAdminCommands commands)
     /// <param name="command">API key administration command to execute.</param>
     /// <param name="output">Text writer for command output.</param>
     /// <param name="cancellationToken">Token to cancel the asynchronous operation.</param>
+    /// <returns>The process exit code for the executed command.</returns>
     public async Task<int> RunAsync(
         ApiKeyAdminCommand command,
         TextWriter output,

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

@@ -6,6 +6,7 @@ public sealed record ApiKeyAdminParseResult(
     string? Error)
 {
     /// <summary>Returns a result indicating the input was not an API key command.</summary>
+    /// <returns>A result with <see cref="IsApiKeyCommand"/> set to <see langword="false"/>.</returns>
     public static ApiKeyAdminParseResult NotApiKeyCommand()
     {
         return new ApiKeyAdminParseResult(false, null, null);
@@ -13,6 +14,7 @@ public sealed record ApiKeyAdminParseResult(
 
     /// <summary>Returns a successful parse result with the parsed API key command.</summary>
     /// <param name="command">Parsed API key administration command.</param>
+    /// <returns>A successful <see cref="ApiKeyAdminParseResult"/> wrapping <paramref name="command"/>.</returns>
     public static ApiKeyAdminParseResult Success(ApiKeyAdminCommand command)
     {
         return new ApiKeyAdminParseResult(true, command, null);
@@ -20,6 +22,7 @@ public sealed record ApiKeyAdminParseResult(
 
     /// <summary>Returns a parse result with the specified error message.</summary>
     /// <param name="error">Error message describing the parse failure.</param>
+    /// <returns>A failed <see cref="ApiKeyAdminParseResult"/> carrying <paramref name="error"/>.</returns>
     public static ApiKeyAdminParseResult Fail(string error)
     {
         return new ApiKeyAdminParseResult(true, null, error);

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

@@ -12,6 +12,7 @@ public static class ApiKeyConstraintSerializer
 
     /// <summary>Serializes API key constraints to JSON, or returns null if the constraints are empty.</summary>
     /// <param name="constraints">The constraints to serialize.</param>
+    /// <returns>The serialized JSON, or <see langword="null"/> when the constraints are empty.</returns>
     public static string? Serialize(ApiKeyConstraints constraints)
     {
         ArgumentNullException.ThrowIfNull(constraints);
@@ -20,6 +21,7 @@ public static class ApiKeyConstraintSerializer
 
     /// <summary>Deserializes API key constraints from JSON, or returns empty constraints if JSON is null or whitespace.</summary>
     /// <param name="json">The JSON string to deserialize.</param>
+    /// <returns>The deserialized constraints, or <see cref="ApiKeyConstraints.Empty"/> when <paramref name="json"/> is null/whitespace.</returns>
     public static ApiKeyConstraints Deserialize(string? json)
     {
         if (string.IsNullOrWhiteSpace(json))

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

@@ -66,10 +66,6 @@ public static class AuthStoreServiceCollectionExtensions
         // migrator and the migration hosted service.
         services.AddZbApiKeyAuth(effectiveConfig, AuthenticationSectionPath);
 
-        // Canonical audit (Task 2.3 — DEEP adopt ZB.MOM.WW.Audit). All MxGateway audit flows as a
-        // canonical AuditEvent through the library IAuditWriter, persisted in a NEW gateway-owned
-        // audit_event table that lives in the SAME SQLite DB file as the api-key stores (it reuses
-        // the library's AuthSqliteConnectionFactory, registered by AddZbApiKeyAuth above).
         services.AddSingleton(sp =>
             new SqliteCanonicalAuditStore(sp.GetRequiredService<AuthSqliteConnectionFactory>()));
         // Resolve the logger defensively: the production host always registers ILogger<T>, but the