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/analyze-message-error-stops-warning-forces-review.bad.al

@@ -0,0 +1,8 @@
+codeunit 50100 "Sales Review Agent Task"
+{
+    procedure AnalyzeAgentTaskMessage(AgentTaskMessage: Record "Agent Task Message"; var Annotations: Record "Agent Annotation")
+    begin
+        // No validation. Combined with SetRequiresReview(false) this auto-runs
+        // untrusted input. Warnings are the only way to force a review later.
+    end;
+}