Add 18 more community AL/BC patterns across appsource, data-modeling, error-handling, security, style, testing, ui, upgrade, and web-services

Second contribution from CURABIS ApS, generalized from patterns observed across real AppSource/PTE development. Cross-checked against the current microsoft/knowledge corpus before opening; several originally-drafted candidates were dropped as duplicates of existing files.

microsoft/knowledge/data-modeling/code-must-not-change-workdate.good.al

@@ -0,0 +1,11 @@
+codeunit 50100 "Posting Date Helper"
+{
+    procedure GetDefaultPostingDate(): Date
+    var
+        PostingDate: Date;
+    begin
+        // Read the work date to default a value; never write to it.
+        PostingDate := WorkDate();
+        exit(PostingDate);
+    end;
+}