docs: add XML doc comments across src + Sister Projects section in CLAUDE.md

Bulk CommentChecker pass: fills in <param>/<inheritdoc> tags on public
APIs across all 23 src/ projects so the doc-coverage gate is green. Also
adds a Sister Projects section to CLAUDE.md pointing at the MxAccess
Gateway and OtOpcUa sibling repos, and gitignores local credential
captures (*login*.txt) and the wonder-app-vd03 deploy/ artifacts.

src/ScadaLink.ExternalSystemGateway/DatabaseGateway.cs

@@ -22,6 +22,12 @@ public class DatabaseGateway : IDatabaseGateway
     private readonly StoreAndForwardService? _storeAndForward;
     private readonly ILogger<DatabaseGateway> _logger;
 
+    /// <summary>
+    /// Initializes a new instance of <see cref="DatabaseGateway"/>.
+    /// </summary>
+    /// <param name="repository">Repository for resolving database connection definitions.</param>
+    /// <param name="logger">Logger for diagnostics.</param>
+    /// <param name="storeAndForward">Optional store-and-forward service for cached writes; null disables buffering.</param>
     public DatabaseGateway(
         IExternalSystemRepository repository,
         ILogger<DatabaseGateway> logger,
@@ -32,10 +38,7 @@ public class DatabaseGateway : IDatabaseGateway
         _storeAndForward = storeAndForward;
     }
 
-    /// <summary>
-    /// Returns an open SqlConnection from the named database connection definition.
-    /// Connection pooling is managed by the underlying ADO.NET provider.
-    /// </summary>
+    /// <inheritdoc />
     public async Task<DbConnection> GetConnectionAsync(
         string connectionName,
         CancellationToken cancellationToken = default)
@@ -66,18 +69,11 @@ public class DatabaseGateway : IDatabaseGateway
     /// Creates the underlying ADO.NET connection for a connection string. Virtual so
     /// tests can substitute a connection whose <c>OpenAsync</c> fails.
     /// </summary>
+    /// <param name="connectionString">The ADO.NET connection string.</param>
     internal virtual DbConnection CreateConnection(string connectionString) =>
         new SqlConnection(connectionString);
 
-    /// <summary>
-    /// Submits a SQL write to the store-and-forward engine for reliable delivery.
-    /// </summary>
-    /// <param name="trackedOperationId">
-    /// Audit Log #23 (M3): used as the S&amp;F message id so the retry loop can
-    /// recover it via <c>StoreAndForwardMessage.Id</c> and emit per-attempt /
-    /// terminal cached-write telemetry (Tasks E4/E5). Null preserves the
-    /// pre-M3 behaviour (S&amp;F mints a random GUID).
-    /// </param>
+    /// <inheritdoc />
     public async Task CachedWriteAsync(
         string connectionName,
         string sql,
@@ -147,6 +143,8 @@ public class DatabaseGateway : IDatabaseGateway
     /// success, false if the connection no longer exists (the message is parked);
     /// throws on any execution error so the engine retries.
     /// </summary>
+    /// <param name="message">The buffered store-and-forward message to deliver.</param>
+    /// <param name="cancellationToken">Cancellation token for the delivery operation.</param>
     public async Task<bool> DeliverBufferedAsync(
         StoreAndForwardMessage message, CancellationToken cancellationToken = default)
     {