Add 18 community AL/BC patterns across style, data-modeling, web-services, appsource, breaking-changes, performance, and testing

Contributed by CURABIS ApS, generalized from patterns observed across real AppSource/PTE development. Each article follows the knowledge file format (frontmatter, Description/Best Practice/Anti Pattern, sibling .good.al/.bad.al samples).

microsoft/knowledge/testing/test-data-must-be-random-and-complete.bad.al

@@ -0,0 +1,14 @@
+[Test]
+procedure PostsSalesOrderForCashCustomer()
+var
+    Customer: Record Customer;
+    SalesHeader: Record "Sales Header";
+begin
+    // Assumes a 'CASH' customer already exists in the environment —
+    // fails on any database where it doesn't.
+    Customer.Get('CASH');
+    LibrarySales.CreateSalesHeader(
+        SalesHeader, SalesHeader."Document Type"::Order, Customer."No.");
+
+    // ... add lines, post, assert ...
+end;