docs: complete XML doc coverage (returns, summaries, inheritdoc)

Resolve all 622 issues flagged by the enhanced CommentChecker: add missing
<returns> tags (incl. the standard phrasing on non-generic Task methods),
add missing <summary> tags, and replace misused/redundant <inheritdoc/> on
members that override or implement nothing with real documentation.
Documentation-only — no behavior change; solution builds clean.

src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/DesignTimeDbContextFactory.cs

@@ -26,6 +26,7 @@ public class DesignTimeDbContextFactory : IDesignTimeDbContextFactory<ScadaBridg
     /// Creates a <see cref="ScadaBridgeDbContext"/> for design-time EF Core tooling.
     /// </summary>
     /// <param name="args">Arguments passed by the EF tooling (unused).</param>
+    /// <returns>A configured <see cref="ScadaBridgeDbContext"/> pointing at the resolved connection string.</returns>
     public ScadaBridgeDbContext CreateDbContext(string[] args)
     {
         var configurationBuilder = new ConfigurationBuilder();

src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/MigrationHelper.cs

@@ -18,6 +18,7 @@ public static class MigrationHelper
     /// <param name="isDevelopment">When true, auto-applies migrations. When false, validates schema version matches.</param>
     /// <param name="logger">Optional logger for readiness-wait diagnostics.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     public static async Task ApplyOrValidateMigrationsAsync(
         ScadaBridgeDbContext dbContext,
         bool isDevelopment,

src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/ServiceCollectionExtensions.cs

@@ -18,6 +18,7 @@ public static class ServiceCollectionExtensions
     /// </summary>
     /// <param name="services">The service collection to register into.</param>
     /// <param name="connectionString">SQL Server connection string for the central configuration database.</param>
+    /// <returns>The same <paramref name="services"/> collection, for chaining.</returns>
     public static IServiceCollection AddConfigurationDatabase(this IServiceCollection services, string connectionString)
     {
         // The DbContext is constructed via the (options, IDataProtectionProvider) overload so
@@ -85,6 +86,7 @@ public static class ServiceCollectionExtensions
     /// <exception cref="InvalidOperationException">
     /// Always thrown. The connection string is required; there is no valid no-op registration.
     /// </exception>
+    /// <returns>Never returns; always throws <see cref="InvalidOperationException"/>.</returns>
     [Obsolete(
         "AddConfigurationDatabase() with no connection string registers nothing and is not a " +
         "valid configuration. Call AddConfigurationDatabase(connectionString) instead.",