feat: Add Drag & Drop support to wxPython GUI

- Implement FileDropTarget class for native file drop handling
- Enable drag and drop for PDF files in the ListBox
- Filter to accept only PDF files with proper validation
- Add user feedback messages when files are dropped
- Store directory of dropped files for next file dialog

gui_wxpython.py

@@ -19,6 +19,34 @@ from update_checker import check_for_updates, get_current_version
 CONFIG_FILE = Path.home() / '.pdf_to_ics_config.json'
 
 
+class FileDropTarget(wx.FileDropTarget):
+    """Custom FileDropTarget für Drag & Drop von PDF-Dateien"""
+    def __init__(self, window):
+        wx.FileDropTarget.__init__(self)
+        self.window = window
+
+    def OnDropFiles(self, x, y, filenames):
+        """Handle für Drag & Drop Events"""
+        pdf_count = 0
+        
+        for filepath in filenames:
+            # Nur PDF-Dateien akzeptieren
+            if filepath.lower().endswith('.pdf'):
+                if filepath not in self.window.pdf_files:
+                    self.window.pdf_files.append(filepath)
+                    self.window.pdf_listbox.Append(Path(filepath).name)
+                    pdf_count += 1
+                    # Merke Verzeichnis
+                    self.window.last_pdf_dir = str(Path(filepath).parent)
+        
+        if pdf_count > 0:
+            self.window.log(f"✓ {pdf_count} PDF-Datei(en) per Drag & Drop hinzugefügt")
+        elif filenames:
+            self.window.log("⚠ Nur PDF-Dateien können hinzugefügt werden")
+        
+        return True
+
+
 class PDFtoICSFrame(wx.Frame):
     def __init__(self):
         super().__init__(parent=None, title='PDF zu ICS Konverter - Dienstplan Importer', size=(800, 700))
@@ -130,6 +158,8 @@ class PDFtoICSFrame(wx.Frame):
         
         # ListBox für PDFs
         self.pdf_listbox = wx.ListBox(panel, style=wx.LB_EXTENDED)
+        # Richte Drag & Drop ein
+        self.pdf_listbox.SetDropTarget(FileDropTarget(self))
         content_sizer.Add(self.pdf_listbox, 1, wx.EXPAND | wx.LEFT | wx.RIGHT, 10)
         
         # Buttons für PDF-Verwaltung