Add community guidance and review support for Business Central agents (#137)

* feat(community/agents): add AL agent quality guidance

- add 20 agent knowledge rules with good and bad AL samples
- clarify setup dialog shape, temporary persistence, permissions, profiles, instructions, capability registration, and interface wiring
- add the community-owned AL agents review skill
- make review fixture discovery layer-aware with custom, community, and Microsoft precedence
- document layer-aware evaluation behavior

* fix(community/agents): align setup and permission samples

- mark agent setup pages as non-extensible where required
- narrow the agent profile by hiding an unrelated sales-order field
- define a dedicated read-only permission set for the sales review agent
- assign AL-defined permission sets with system scope and the owning app ID
- clarify the permission scope guidance for default access controls

* Address agent review feedback

community/knowledge/agents/bind-agent-subscribers-only-in-agent-session.good.al

@@ -0,0 +1,34 @@
+codeunit 50101 "Sales Review Agent Subscribers"
+{
+    Access = Internal;
+    EventSubscriberInstance = Manual;
+    SingleInstance = true;
+
+    [EventSubscriber(ObjectType::Table, Database::"Sales Header", OnAfterInsertEvent, '', false, false)]
+    local procedure OnAfterInsertSalesHeader(var Rec: Record "Sales Header")
+    begin
+        Message('Keep going, agent.');
+    end;
+}
+
+codeunit 50102 "Agent Session Events"
+{
+    Access = Internal;
+    SingleInstance = true;
+    InherentEntitlements = X;
+    InherentPermissions = X;
+
+    var
+        GlobalAgentSubscribers: Codeunit "Sales Review Agent Subscribers";
+
+    [EventSubscriber(ObjectType::Codeunit, Codeunit::"System Initialization", OnAfterInitialization, '', false, false)]
+    local procedure RegisterSubscribersOnAfterInitialization()
+    var
+        AgentSession: Codeunit "Agent Session";
+        AgentMetadataProvider: Enum "Agent Metadata Provider";
+    begin
+        if not AgentSession.IsAgentSession(AgentMetadataProvider) then
+            exit;
+        if BindSubscription(GlobalAgentSubscribers) then;
+    end;
+}