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/cross-app-agent-calls-need-your-public-api.bad.al

@@ -0,0 +1,10 @@
+codeunit 50110 "Other App Agent Hook"
+{
+    procedure RenameForeignAgent(AgentUserSecurityId: Guid)
+    var
+        Agent: Codeunit Agent;
+    begin
+        // Fails at runtime when the instance was defined in another app.
+        Agent.SetDisplayName(AgentUserSecurityId, 'Updated Name');
+    end;
+}