Add events knowledge domain and review leaf skill

Add a new `events` knowledge domain covering AL events & subscribers,
wired into the AL review pipeline.

- 3 atomic articles (+ .good.al/.bad.al samples) under
  microsoft/knowledge/events/: the IsHandled override pattern, thin
  OnBefore/OnAfter integration-event publishers, and static vs manual
  subscribers.
- New leaf skill microsoft/skills/review/al-events-review.md sourcing the
  events domain.
- Wired into microsoft/skills/review/al-code-review.md (sub-skills + Source
  + description) and README.md (leaf-skill count + domain list).

AL event syntax verified against Microsoft Learn. Samples are
demonstration-only (not compiled by CI). Additive change; no contract change.

Part of #34.

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

microsoft/knowledge/events/use-ishandled-to-make-base-behaviour-overridable.good.al

@@ -0,0 +1,37 @@
+// Demonstration-only AL. Not compiled by CI; illustrates the article.
+codeunit 50220 "Shipping Charge Good Sample"
+{
+    procedure CalculateShippingCharge(OrderAmount: Decimal) Charge: Decimal
+    var
+        IsHandled: Boolean;
+    begin
+        // Give extensions a sanctioned seam to replace the calculation, then
+        // skip the default logic when a subscriber has handled it.
+        OnBeforeCalculateShippingCharge(OrderAmount, Charge, IsHandled);
+        if IsHandled then
+            exit(Charge);
+
+        if OrderAmount >= 1000 then
+            Charge := 0
+        else
+            Charge := 49;
+    end;
+
+    [IntegrationEvent(false, false)]
+    local procedure OnBeforeCalculateShippingCharge(OrderAmount: Decimal; var Charge: Decimal; var IsHandled: Boolean)
+    begin
+    end;
+}
+
+codeunit 50221 "Shipping Charge Sub Good Sample"
+{
+    // A partner replaces the flat rate with a contract-specific rule.
+    [EventSubscriber(ObjectType::Codeunit, Codeunit::"Shipping Charge Good Sample", 'OnBeforeCalculateShippingCharge', '', false, false)]
+    local procedure ApplyContractRate(OrderAmount: Decimal; var Charge: Decimal; var IsHandled: Boolean)
+    begin
+        if IsHandled then
+            exit;
+        Charge := OrderAmount * 0.02;
+        IsHandled := true;
+    end;
+}