knowledge(performance): add community rules for JIT, locks, and false positives

These articles capture BC-specific mechanics agents still invert: partial-record JIT on writes, Reset clearing SetLoadFields, HttpClient inside write transactions, and batched number series, plus negative guidance that stops over-eager Query and IsEmpty "fixes".

Co-authored-by: Cursor <cursoragent@cursor.com>

community/knowledge/performance/page-background-tasks-for-expensive-cues.bad.al

@@ -0,0 +1,31 @@
+page 50100 "Cue Background Task Bad"
+{
+    PageType = CardPart;
+    ApplicationArea = All;
+
+    layout
+    {
+        area(content)
+        {
+            cuegroup(Group)
+            {
+                field(OpenOrders; OpenOrderCount)
+                {
+                    Caption = 'Open Sales Orders';
+                }
+            }
+        }
+    }
+
+    var
+        OpenOrderCount: Integer;
+
+    trigger OnOpenPage()
+    var
+        SalesHeader: Record "Sales Header";
+    begin
+        // Blocks Role Center render on an exact count of sales headers.
+        SalesHeader.SetRange("Document Type", SalesHeader."Document Type"::Order);
+        OpenOrderCount := SalesHeader.Count();
+    end;
+}