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/advimage/langs/en_dlg.js

@@ -0,0 +1 @@
+tinyMCE.addI18n('en.advimage_dlg',{"image_list":"Image List","align_right":"Right","align_left":"Left","align_textbottom":"Text Bottom","align_texttop":"Text Top","align_bottom":"Bottom","align_middle":"Middle","align_top":"Top","align_baseline":"Baseline",align:"Alignment",hspace:"Horizontal Space",vspace:"Vertical Space",dimensions:"Dimensions",border:"Border",list:"Image List",alt:"Image Description",src:"Image URL","dialog_title":"Insert/Edit Image","missing_alt":"Are you sure you want to continue without including an Image Description? Without it the image may not be accessible to some users with disabilities, or to those using a text browser, or browsing the Web with images turned off.","example_img":"Appearance Preview Image",misc:"Miscellaneous",mouseout:"For Mouse Out",mouseover:"For Mouse Over","alt_image":"Alternative Image","swap_image":"Swap Image",map:"Image Map",id:"ID",rtl:"Right to Left",ltr:"Left to Right",classes:"Classes",style:"Style","long_desc":"Long Description Link",langcode:"Language Code",langdir:"Language Direction","constrain_proportions":"Constrain Proportions",preview:"Preview",title:"Title",general:"General","tab_advanced":"Advanced","tab_appearance":"Appearance","tab_general":"General",width:"Width",height:"Height"});