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/httpclient-inside-write-transaction-holds-locks.bad.al

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+codeunit 50100 "HttpClient Holds Locks Bad"
+{
+    procedure SyncCustomerLastName(var Customer: Record Customer)
+    var
+        Client: HttpClient;
+        Response: HttpResponseMessage;
+    begin
+        Customer."Search Name" := Customer.Name;
+        Customer.Modify(false);
+        // Locks from Modify are held for the entire HTTP wait.
+        Client.Get(StrSubstNo('https://example.local/sync/%1', Customer."No."), Response);
+    end;
+}