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.ConfigurationDatabase/ServiceCollectionExtensions.cs

@@ -16,6 +16,8 @@ public static class ServiceCollectionExtensions
     /// <summary>
     /// Registers the ScadaLinkDbContext with the provided SQL Server connection string.
     /// </summary>
+    /// <param name="services">The service collection to register into.</param>
+    /// <param name="connectionString">SQL Server connection string for the central configuration database.</param>
     public static IServiceCollection AddConfigurationDatabase(this IServiceCollection services, string connectionString)
     {
         // The DbContext is constructed via the (options, IDataProtectionProvider) overload so
@@ -76,6 +78,7 @@ public static class ServiceCollectionExtensions
     /// <see cref="AddConfigurationDatabase(IServiceCollection, string)"/> and pass the
     /// configured connection string.
     /// </summary>
+    /// <param name="services">The service collection (unused; this overload always throws).</param>
     /// <exception cref="InvalidOperationException">
     /// Always thrown. The connection string is required; there is no valid no-op registration.
     /// </exception>