fix(scheduler): add to_dict to AnimeSeries for auto-download

AnimeSeries objects returned by SerieList.GetMissingEpisode() lacked
to_dict(), causing AttributeError when _run_auto_download() called
series.get("episodeDict").

src/server/database/models.py

@@ -13,7 +13,7 @@ from __future__ import annotations
 
 from datetime import datetime, timezone
 from enum import Enum
-from typing import List, Optional
+from typing import Any, Dict, List, Optional
 
 from sqlalchemy import Boolean, DateTime, ForeignKey, Index, Integer, String, Text, func
 from sqlalchemy.orm import Mapped, mapped_column, relationship, validates
@@ -247,6 +247,21 @@ class AnimeSeries(Base, TimestampMixin):
         except ValueError:
             return sanitize_folder_name(self.key)
 
+    def to_dict(self) -> Dict[str, Any]:
+        """Convert to dictionary for cache serialization.
+
+        Returns:
+            Dictionary with series data including episodeDict for
+            auto-download functionality.
+        """
+        return {
+            "key": self.key,
+            "name": self.name,
+            "site": self.site,
+            "folder": self.folder,
+            "episodeDict": self.episodeDict,
+        }
+
 
 class Episode(Base, TimestampMixin):
     """SQLAlchemy model for anime episodes.