fix: use Path(__file__).parent instead of Path.cwd() in TranslationSystem

Default app_dir in TranslationSystem.__init__ was Path.cwd(), which
breaks when the app is launched from a different working directory
(e.g. double-click, compiled EXE, or other CWD).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Lukas Geiger

translator.py

@@ -28,12 +28,12 @@ def __init__(self, default_lang: str = 'de', app_dir: Path = None):
 
         Args:
             default_lang: Standard-Sprache ('de' oder 'en')
-            app_dir: Verzeichnis der Anwendung (default: aktuelles Verzeichnis)
+            app_dir: Verzeichnis der Anwendung (default: Verzeichnis dieser Datei)
         """
         self.current_lang = default_lang
 
         if app_dir is None:
-            app_dir = Path.cwd()
+            app_dir = Path(__file__).parent
         self.app_dir = Path(app_dir)
 
         self.translations_file = self.app_dir / "locales" / "translations.json"