Fix get_all_series_from_data_files to read data files directly

Previously, the method created a SerieList instance which only loads
from database, not from data files. Now reads data files directly
and parses JSON to create AnimeSeries objects.

Also added _load_data_file helper function and fixed logger.warning
calls to use proper format strings instead of keyword arguments.

Updated unit tests to use real temp directories instead of mocks.

src/server/SeriesApp.py

@@ -697,11 +697,15 @@ class SeriesApp:
             self.directory_to_search
         )
 
-        # Create a fresh SerieList instance for file-based loading
-        # This ensures we get all series from data files without
-        # interfering with the main instance's state
+        all_series: List[AnimeSeries] = []
+
         try:
-            temp_list = SerieList(self.directory_to_search)
+            if not os.path.isdir(self.directory_to_search):
+                logger.warning(
+                    "Directory does not exist: %s",
+                    self.directory_to_search
+                )
+                return []
         except (OSError, ValueError) as e:
             logger.error(
                 "Failed to scan directory for data files: %s",
@@ -710,8 +714,53 @@ class SeriesApp:
             )
             return []
 
-        # Get all series from the temporary list
-        all_series = temp_list.get_all()
+        try:
+            for folder_name in os.listdir(self.directory_to_search):
+                folder_path = os.path.join(
+                    self.directory_to_search, folder_name
+                )
+                if not os.path.isdir(folder_path):
+                    continue
+
+                data_file = os.path.join(folder_path, "data")
+                if not os.path.isfile(data_file):
+                    continue
+
+                series_data = _load_data_file(data_file)
+                if series_data is None:
+                    continue
+
+                key = series_data.get("key")
+                if not key:
+                    logger.warning(
+                        "Data file missing key, skipping: %s",
+                        data_file
+                    )
+                    continue
+
+                anime = AnimeSeries(
+                    key=key,
+                    name=series_data.get("name") or folder_name,
+                    site=series_data.get("site", "https://aniworld.to"),
+                    folder=series_data.get("folder", folder_name),
+                    year=series_data.get("year"),
+                )
+
+                episode_dict = series_data.get("episodeDict", {})
+                if episode_dict:
+                    anime._episode_dict_cache = {
+                        int(season): episodes
+                        for season, episodes in episode_dict.items()
+                    }
+
+                all_series.append(anime)
+        except (OSError, ValueError) as e:
+            logger.error(
+                "Failed to scan directory for data files: %s",
+                str(e),
+                exc_info=True
+            )
+            return []
 
         logger.info(
             "Found %d series from data files in %s",
@@ -731,3 +780,38 @@ class SeriesApp:
         if hasattr(self, 'executor'):
             self.executor.shutdown(wait=True)
             logger.info("ThreadPoolExecutor shut down successfully")
+
+
+def _load_data_file(data_file_path: str) -> Optional[dict]:
+    """Load and parse a legacy 'data' file (JSON).
+
+    Args:
+        data_file_path: Path to the data file
+
+    Returns:
+        Parsed data dict or None if parsing fails
+    """
+    import json
+
+    try:
+        with open(data_file_path, "r", encoding="utf-8") as f:
+            data = json.load(f)
+
+        if not isinstance(data, dict):
+            logger.warning("Data file is not a dictionary: %s", data_file_path)
+            return None
+
+        return data
+
+    except json.JSONDecodeError as e:
+        logger.warning(
+            "Failed to parse legacy data file (JSON error): %s - %s",
+            data_file_path, str(e)
+        )
+        return None
+    except Exception as e:
+        logger.warning(
+            "Failed to read legacy data file: %s - %s",
+            data_file_path, str(e)
+        )
+        return None