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.CentralUI/Components/Pages/Design/TransportImport.razor.cs

@@ -353,6 +353,8 @@ public partial class TransportImport : ComponentBase
     /// </list>
     /// Visible to tests via <c>internal</c> so the default-mapping contract is unit-pinned.
     /// </summary>
+    /// <param name="preview">The import preview containing all conflict items to map.</param>
+    /// <returns>A dictionary keyed by (EntityType, Name) with default resolution actions populated.</returns>
     internal static Dictionary<(string EntityType, string Name), ImportResolution> BuildDefaultResolutions(
         ImportPreview preview)
     {