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/prefer-interface-over-case-branching.bad.al

@@ -0,0 +1,32 @@
+enum 50204 "Shipping Method Bad"
+{
+    Extensible = true;
+
+    value(0; Standard) { }
+    value(1; Express) { }
+}
+
+codeunit 50205 "Shipping Charge Bad"
+{
+    // Anti-pattern: every call site must 'case' over the enum, and every new
+    // shipping method forces a synchronized edit to each of these blocks.
+    procedure GetRate(Method: Enum "Shipping Method Bad"; Weight: Decimal): Decimal
+    begin
+        case Method of
+            Method::Standard:
+                exit(Weight * 1.5);
+            Method::Express:
+                exit((Weight * 1.5) + 25);
+        end;
+    end;
+
+    procedure GetDeliveryDays(Method: Enum "Shipping Method Bad"): Integer
+    begin
+        case Method of
+            Method::Standard:
+                exit(5);
+            Method::Express:
+                exit(1);
+        end;
+    end;
+}