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.CLI/Commands/DataConnectionCommands.cs

@@ -6,6 +6,13 @@ namespace ScadaLink.CLI.Commands;
 
 public static class DataConnectionCommands
 {
+    /// <summary>
+    /// Builds the <c>data-connection</c> command group and all its subcommands.
+    /// </summary>
+    /// <param name="urlOption">Global management URL option.</param>
+    /// <param name="formatOption">Global output format option.</param>
+    /// <param name="usernameOption">Global username option.</param>
+    /// <param name="passwordOption">Global password option.</param>
     public static Command Build(Option<string> urlOption, Option<string> formatOption, Option<string> usernameOption, Option<string> passwordOption)
     {
         var command = new Command("data-connection") { Description = "Manage data connections" };