Initialer Commit: Kundenverwaltung (PHP/Smarty)

Bestehende Codebasis als Ausgangsstand aufgenommen.

- .gitignore: Kundendaten (uploads_*), Smarty-Compile-Cache
  (templates_c), Laufzeit-Temp und Datenbank-Dumps ausgeschlossen;
  Verzeichnisstruktur ueber .gitkeep erhalten
- .gitattributes: Zeilenenden normalisiert (LF im Repo),
  Binaerformate markiert
- db-backup.php: MySQL-Zugangsdaten kommen jetzt wie im Rest der
  Anwendung aus der externen Konfiguration statt hartkodiert aus der
  Datei; Passwort wird ueber eine temporaere Optionsdatei statt per
  Kommandozeile uebergeben, Fehler von mysqldump/gzip werden gemeldet,
  Aufraeumen aelterer Backups berechnet Jahr und Monat konsistent

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

js/tiny_mce/plugins/advlink/langs/en_dlg.js

@@ -0,0 +1 @@
+tinyMCE.addI18n('en.advlink_dlg',{"target_name":"Target Name",classes:"Classes",style:"Style",id:"ID","popup_position":"Position (X/Y)",langdir:"Language Direction","popup_size":"Size","popup_dependent":"Dependent (Mozilla/Firefox Only)","popup_resizable":"Make Window Resizable","popup_location":"Show Location Bar","popup_menubar":"Show Menu Bar","popup_toolbar":"Show Toolbars","popup_statusbar":"Show Status Bar","popup_scrollbars":"Show Scrollbars","popup_return":"Insert \'return false\'","popup_name":"Window Name","popup_url":"Popup URL",popup:"JavaScript Popup","target_blank":"Open in New Window","target_top":"Open in Top Frame (Replaces All Frames)","target_parent":"Open in Parent Window/Frame","target_same":"Open in This Window/Frame","anchor_names":"Anchors","popup_opts":"Options","advanced_props":"Advanced Properties","event_props":"Events","popup_props":"Popup Properties","general_props":"General Properties","advanced_tab":"Advanced","events_tab":"Events","popup_tab":"Popup","general_tab":"General",list:"Link List","is_external":"The URL you entered seems to be an external link. Do you want to add the required http:// prefix?","is_email":"The URL you entered seems to be an email address. Do you want to add the required mailto: prefix?",titlefield:"Title",target:"Target",url:"Link URL",title:"Insert/Edit Link","link_list":"Link List",rtl:"Right to Left",ltr:"Left to Right",accesskey:"AccessKey",tabindex:"TabIndex",rev:"Relationship Target to Page",rel:"Relationship Page to Target",mime:"Target MIME Type",encoding:"Target Character Encoding",langcode:"Language Code","target_langcode":"Target Language",width:"Width",height:"Height"});