Add interfaces knowledge domain and review leaf skill (#42)

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: Jesper Schulz-Wedde <jesper.schulzwedde@microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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

@@ -0,0 +1,49 @@
+interface INotifier
+{
+    procedure Send(Recipient: Text; Body: Text): Boolean;
+}
+
+codeunit 50206 "Email Notifier" implements INotifier
+{
+    procedure Send(Recipient: Text; Body: Text): Boolean
+    begin
+        // A real implementation would hand the message to an email service.
+        exit(Recipient <> '');
+    end;
+}
+
+codeunit 50207 "Default Notifier" implements INotifier
+{
+    procedure Send(Recipient: Text; Body: Text): Boolean
+    begin
+        // Safe fallback so an unmapped or future channel still resolves to a
+        // usable object instead of failing where the interface is called.
+        exit(false);
+    end;
+}
+
+enum 50208 "Notification Channel" implements INotifier
+{
+    Extensible = true;
+    DefaultImplementation = INotifier = "Default Notifier";
+
+    value(0; Email)
+    {
+        Implementation = INotifier = "Email Notifier";
+    }
+    value(1; None)
+    {
+        // No explicit Implementation: resolves to DefaultImplementation above.
+    }
+}
+
+codeunit 50209 "Notification Dispatch"
+{
+    procedure Notify(Channel: Enum "Notification Channel"; Recipient: Text; Body: Text): Boolean
+    var
+        Notifier: Interface INotifier;
+    begin
+        Notifier := Channel;
+        exit(Notifier.Send(Recipient, Body));
+    end;
+}