feat(anime): add year to folder names on series add

- Add _compute_folder_name helper that deduplicates year (handles cases like 'Name (2023)' not becoming 'Name (2023) (2023)')
- Create anime folder on disk when adding series (not just DB + memory)
- Add rename_folder_if_needed to auto-rename existing folders without year
- Fetch year from aniworld_provider and include in folder as 'Name (YYYY)'

Closes: anime folders now include release year when available from provider

src/server/services/anime_service.py

@@ -1204,6 +1204,100 @@ class AnimeService:
         
         return anime_series
 
+    async def rename_folder_if_needed(
+        self,
+        key: str,
+        current_folder: str,
+        target_folder: str,
+        db: Optional[AsyncSession] = None,
+    ) -> bool:
+        """Rename anime folder if current and target folders differ.
+
+        Compares current_folder with target_folder, and if different,
+        renames the folder on disk using shutil.move. Updates the DB
+        record and in-memory cache if rename succeeds.
+
+        Args:
+            key: Series unique identifier
+            current_folder: Current folder name (metadata from DB)
+            target_folder: Desired folder name (computed with year)
+            db: Optional database session for updating DB record
+
+        Returns:
+            True if rename was performed, False if no rename needed or failed
+        """
+        import os
+        import shutil
+
+        if current_folder == target_folder:
+            logger.debug(
+                "Folder rename not needed for %s: same folder name",
+                key
+            )
+            return False
+
+        current_path = self._directory / current_folder
+        target_path = self._directory / target_folder
+
+        if not current_path.exists():
+            logger.debug(
+                "Folder rename not needed for %s: current folder does not exist on disk",
+                key
+            )
+            return False
+
+        if target_path.exists():
+            logger.warning(
+                "Cannot rename folder for %s: target path already exists: %s",
+                key,
+                target_path
+            )
+            return False
+
+        try:
+            # Rename folder on disk
+            shutil.move(str(current_path), str(target_path))
+            logger.info(
+                "Renamed folder for %s: %s -> %s",
+                key,
+                current_folder,
+                target_folder
+            )
+
+            # Update in-memory cache
+            if key in self._app.list.keyDict:
+                self._app.list.keyDict[key].folder = target_folder
+                logger.debug(
+                    "Updated in-memory cache folder for %s: %s",
+                    key,
+                    target_folder
+                )
+
+            # Update database if session provided
+            if db is not None:
+                from src.server.database.service import AnimeSeriesService
+
+                # Look up series by key to get database ID
+                series = await AnimeSeriesService.get_by_key(db, key)
+                if series:
+                    await AnimeSeriesService.update(db, series_id=series.id, folder=target_folder)
+                    logger.debug(
+                        "Updated DB folder for %s: %s",
+                        key,
+                        target_folder
+                    )
+
+            return True
+
+        except Exception as e:
+            logger.exception(
+                "Failed to rename folder for %s: %s -> %s",
+                key,
+                current_folder,
+                target_folder
+            )
+            return False
+
     async def contains_in_db(self, key: str, db) -> bool:
         """
         Check if a series with the given key exists in the database.