Use setenv in launcher scripts, add requirements.txt and missing .sh scripts

platz.bat/platz.sh now derive PLATZ via setenv instead of hardcoded
paths, matching the Standard Programm Template already applied to
setenv/install_py/activate_venv/get_cmd. Added the missing .sh
counterparts to those .bat scripts, an empty requirements.txt for
install_py to install (project only uses the stdlib), and ignore
entries for .venv/, out/, .vscode/, *.swp.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

requirements.txt

@@ -0,0 +1,8 @@
+# Python-Abhaengigkeiten fuer platz
+#
+# Aktuell werden nur Module aus der Standardbibliothek verwendet
+# (ConfigParser, xml.dom.minidom, sets, UserList, random, ...).
+# Keine externen Pakete erforderlich.
+#
+# Beispiel:
+# requests==2.31.0