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/style/fixed-choice-set-must-use-enum-not-integer.bad.al

@@ -0,0 +1,22 @@
+table 50101 "Course"
+{
+    fields
+    {
+        field(1; "No."; Code[20]) { }
+        // 1 = Beginner, 2..3 = Intermediate, 4+ = Advanced
+        field(10; Difficulty; Integer) { }
+    }
+}
+
+codeunit 50100 "Course Level Helper"
+{
+    procedure LevelText(Difficulty: Integer): Text
+    begin
+        case Difficulty of
+            1:
+                exit('Beginner');
+            2, 3:
+                exit('Intermediate');
+        end;
+    end;
+}