Codebasis als Dateien ins Arbeitsrepo statt als Gitlink

QuellCode/CentronERP war nur als Gitlink (Submodul-Referenz auf 79c1142)
getrackt, ohne .gitmodules und ohne erreichbares Remote. Der
Untersuchungsgegenstand der Versuchsreihe war damit nicht reproduzierbar
gesichert: Ein Klon haette ein leeres Verzeichnis erhalten, und die Belege
der 3.287 Anforderungen waeren nicht ueberpruefbar gewesen.

Umstellung:
- Historie nach c:\DEV\CentronERP_git_snapshot_79c1142 ausgelagert
  (vollstaendig lesbar, enthaelt 79c1142 und Vorgaenger 89ccfd6)
- Gitlink aus dem Index entfernt
- Dateiinhalt aufgenommen: 24.557 Dateien, rund 333 MB

Die verschachtelte .gitignore der Codebasis gilt weiter, Build-Artefakte
bleiben ausgeschlossen. Details in Versuche/Versuch_01/_Codebasis-Nachweis.md

QuellCode/CentronERP/docs/reference/security/developer-security.md

@@ -0,0 +1,25 @@
+# Developer security
+
+We have some security in place, to protect developers from accidentally doing something bad, for example sending mails to real customers.  
+
+These safeguards can't protect you from all accidents, so you still have to be careful when you're sending mails or calling external APIs.  
+But in most cases, you should be protected and safe.
+
+All of these safeguards are configured in the `DeveloperSecurity.cs` file.  
+Check out the code in that file to get a detailed understanding of how it works and what it does.
+
+## Sending emails
+
+To protect us from accidentally sending emails to actual customer email addresses, there are some safeguards in place.  
+
+> :exclamation: These safeguards are only active in DEBUG-builds of the c-entron.NET :exclamation:
+
+If you manually create a RELEASE-build of the c-entron.NET and send emails with it, it's up to you to as the developer to make sure that you don't send any emails to actual customer email addresses.  
+
+In DEBUG-builds all **external email addresses** will get replaced by `test@nexoware.com`.  
+The **internal email addresses** will not get modified at all.  
+
+> A email address is considered **internal** when it ends with `nexoware.com`.  
+> Every other email address is considered **external**.
+
+If you want to disable this behavior (for example when you're trying to test your email sending code), you can manually edit the `AllowSendingEmailToExternalAddresses` property in the `DeveloperSecurity.cs` file.