Add interfaces knowledge domain and review leaf skill

Adds the interfaces knowledge domain covering AL interfaces and enum-with-implementation: three atomic articles with good/bad AL samples, a new al-interfaces-review leaf skill, and additive wiring into al-code-review and the README. Purely additive; no contract change.

Part of #34.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

microsoft/knowledge/interfaces/set-defaultimplementation-on-enum.bad.al

@@ -0,0 +1,39 @@
+interface INotifier
+{
+    procedure Send(Recipient: Text; Body: Text): Boolean;
+}
+
+codeunit 50210 "Email Notifier Bad" implements INotifier
+{
+    procedure Send(Recipient: Text; Body: Text): Boolean
+    begin
+        exit(Recipient <> '');
+    end;
+}
+
+enum 50211 "Notification Channel Bad" implements INotifier
+{
+    Extensible = true;
+    // No DefaultImplementation declared.
+
+    value(0; Email)
+    {
+        Implementation = INotifier = "Email Notifier Bad";
+    }
+    value(1; None)
+    {
+        // No Implementation here and no enum-level DefaultImplementation:
+        // resolving this value to INotifier and calling Send fails at runtime.
+    }
+}
+
+codeunit 50212 "Notification Dispatch Bad"
+{
+    procedure Notify(Channel: Enum "Notification Channel Bad"; Recipient: Text; Body: Text): Boolean
+    var
+        Notifier: Interface INotifier;
+    begin
+        Notifier := Channel;                    // Channel::None has no implementation
+        exit(Notifier.Send(Recipient, Body));   // runtime failure for the None value
+    end;
+}