rewrite comments in neutral, terse style

Doc comments, inline comments, and README no longer editorialize about
the code (ActiveRecord, leak, fake, Yak before/after). They now describe
behavior only. Test A_client_can_reach_its_DbContext__the_leak renamed
to A_client_can_reach_its_DbContext. No behavior changes; all 27 tests
pass.

src/Before/Order.cs

@@ -1,20 +1,11 @@
 namespace Before;
 
-/// <summary>
-/// An order, backed by the database: it derives from <see cref="DbBase"/> and
-/// holds a back-reference to its <see cref="Client"/> (the other end of the
-/// relation). In the "after" situation this becomes a plain POCO with an
-/// <c>OrderDto</c> carrying its data to the WebApp.
-/// </summary>
+/// <summary>An order belonging to a <see cref="Client"/>.</summary>
 public class Order : DbBase
 {
-    /// <summary>Free-text description of what this order is for.</summary>
+    /// <summary>Free-text description.</summary>
     public string Description { get; set; } = string.Empty;
 
-    /// <summary>
-    /// The client that owns this order. Set automatically by
-    /// <see cref="ClientOrders"/> when the order is added to
-    /// <see cref="Client.Orders"/> (navigation fix-up).
-    /// </summary>
+    /// <summary>The owning client; set by <see cref="ClientOrders"/>.</summary>
     public Client? Client { get; set; }
 }