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/instruction-structure-is-role-rules-steps.good.al

@@ -0,0 +1,17 @@
+codeunit 50100 "Sales Review Agent Instr."
+{
+    procedure GetInstructions() Instructions: SecretText
+    var
+        Builder: TextBuilder;
+    begin
+        Builder.AppendLine('# Responsibilities');
+        Builder.AppendLine('You validate sales orders against customer credit and hold status.');
+        Builder.AppendLine('# Guidelines');
+        Builder.AppendLine('Always request a review before posting or sending external mail.');
+        Builder.AppendLine('# Instructions');
+        Builder.AppendLine('1. Open the sales order named in the task.');
+        Builder.AppendLine('2. Check credit limit and overdue balance.');
+        Builder.AppendLine('3. Document the result on the order and request a review.');
+        Instructions := Builder.ToText();
+    end;
+}