Refactor: Defer folder creation to download time

- Remove folder creation from add_series endpoint
- Add folder creation to download() method in SeriesApp
- Maintain database persistence and targeted scanning
- Update tests to use tmp_path fixtures
- All add_series and download tests passing (13/13)

src/core/SeriesApp.py

@@ -12,6 +12,7 @@ Note:
 
 import asyncio
 import logging
+import os
 from concurrent.futures import ThreadPoolExecutor
 from typing import Any, Dict, List, Optional
 
@@ -317,6 +318,36 @@ class SeriesApp:
             )
         )
 
+        # Create series folder if it doesn't exist
+        folder_path = os.path.join(self.directory_to_search, serie_folder)
+        if not os.path.exists(folder_path):
+            try:
+                os.makedirs(folder_path, exist_ok=True)
+                logger.info(
+                    "Created series folder: %s (key: %s)",
+                    folder_path,
+                    key
+                )
+            except OSError as e:
+                logger.error(
+                    "Failed to create series folder %s: %s",
+                    folder_path,
+                    str(e)
+                )
+                # Fire download failed event
+                self._events.download_status(
+                    DownloadStatusEventArgs(
+                        serie_folder=serie_folder,
+                        key=key,
+                        season=season,
+                        episode=episode,
+                        status="failed",
+                        message=f"Failed to create folder: {str(e)}",
+                        item_id=item_id,
+                    )
+                )
+                return False
+
         try:
             def download_progress_handler(progress_info):
                 """Handle download progress events from loader."""