Fix Concept section: use IsFullyPaid() example, not custom matcher

The Concept demo should show a different pattern (encapsulate behavior)
than the exercise (custom matcher) so the exercise stays fresh.

exercises/show-dont-tell/learning-hour.md

@@ -44,10 +44,10 @@ The agent might:
 
 ### The "Show" Approach (works better)
 
-Refactor one test yourself:
+Refactor one test yourself — encapsulate the attribute check behind a behavior method:
 
 ```csharp
-// Before — telling attributes
+// Before — checking an attribute
 [Test]
 public void CompletedOrder_TotalIsCorrect()
 {
@@ -56,7 +56,6 @@ public void CompletedOrder_TotalIsCorrect()
     order.Complete();
 
     Assert.That(order.Total, Is.EqualTo(100m));
-    Assert.That(order.Status, Is.EqualTo("completed"));
 }
 
 // After — encapsulating behavior
@@ -67,13 +66,13 @@ public void CompletedOrder_TotalIsCorrect()
     order.AddLine(100m, 1);
     order.Complete();
 
-    Assert.That(order, Has.OrderTotalCorrect(100m));
+    Assert.That(order.IsFullyPaid(100m), Is.True);
 }
 ```
 
 Then ask the agent:
 
-> The first test was refactored to use `Has.OrderTotalCorrect()`. Apply the same pattern to the remaining tests.
+> The first test was refactored to use `order.IsFullyPaid(expected)` instead of asserting on `order.Total`. Apply the same pattern to the remaining tests.
 
 The agent sees the concrete pattern and replicates it. No description needed.