Add breaking-changes knowledge domain and review leaf skill

Seed a new breaking-changes (AL API stability) knowledge domain with six
articles plus good/bad AL samples, a new al-breaking-changes-review leaf
skill, and minimal wiring into al-code-review and the README.

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

microsoft/knowledge/breaking-changes/do-not-expose-sensitive-data-through-public-api.good.al

@@ -0,0 +1,25 @@
+codeunit 50320 "Payment Client Good"
+{
+    var
+        AccessToken: Text;
+
+    // Credential flows inward through an internal setter and never leaves the object.
+    internal procedure SetAccessToken(NewToken: Text)
+    begin
+        AccessToken := NewToken;
+    end;
+
+    // Public API exposes only non-sensitive data — a masked reference, never the token.
+    procedure GetMaskedReference(): Text
+    var
+        Reference: Text;
+    begin
+        Reference := LastReference();
+        exit('****-' + CopyStr(Reference, StrLen(Reference) - 3));
+    end;
+
+    local procedure LastReference(): Text
+    begin
+        exit('REF000123456');
+    end;
+}