fix: add episodeDict setter to AnimeSeries model

SerieScanner attempted to assign serie.episodeDict = missing_episodes
but the property had no setter, causing AttributeError during scan.

Added setter that stores value in _episode_dict_cache, which the getter
already checks. This allows SerieScanner to update episodeDict directly.

src/server/database/models.py

@@ -210,6 +210,15 @@ class AnimeSeries(Base, TimestampMixin):
                 episode_dict[season].append(ep.episode_number or 0)
         return episode_dict
 
+    @episodeDict.setter
+    def episodeDict(self, value: dict[int, list[int]]) -> None:
+        """Set the episode dictionary via private cache.
+
+        Args:
+            value: Dictionary mapping season numbers to lists of episode numbers
+        """
+        self._episode_dict_cache = value
+
     @property
     def name_with_year(self) -> str:
         """Get series name with year appended if available.