Add data file to database sync functionality

- Add get_all_series_from_data_files() to SeriesApp
- Sync series from data files to DB on startup
- Add unit tests for new SeriesApp method
- Add integration tests for sync functionality
- Update documentation

src/server/fastapi_app.py

@@ -41,6 +41,78 @@ from src.server.services.websocket_service import get_websocket_service
 # module-level globals. This makes testing and multi-instance hosting safer.
 
 
+async def _sync_series_to_database(
+    anime_directory: str,
+    logger
+) -> int:
+    """
+    Sync series from data files to the database.
+    
+    Scans the anime directory for data files and adds any new series
+    to the database. Existing series are skipped (no duplicates).
+    
+    Args:
+        anime_directory: Path to the anime directory with data files
+        logger: Logger instance for logging operations
+        
+    Returns:
+        Number of new series added to the database
+    """
+    try:
+        import asyncio
+
+        from src.core.entities.SerieList import SerieList
+        from src.core.SeriesApp import SeriesApp
+        from src.server.database.connection import get_db_session
+
+        # Get all series from data files using SeriesApp
+        series_app = SeriesApp(anime_directory)
+        all_series = await asyncio.to_thread(
+            series_app.get_all_series_from_data_files
+        )
+
+        if not all_series:
+            logger.info("No series found in data files to sync")
+            return 0
+
+        logger.info(
+            "Found %d series in data files, syncing to database...",
+            len(all_series)
+        )
+
+        async with get_db_session() as db:
+            serie_list = SerieList(
+                anime_directory,
+                db_session=db,
+                skip_load=True
+            )
+            added_count = 0
+            for serie in all_series:
+                result = await serie_list.add_to_db(serie, db)
+                if result:
+                    added_count += 1
+                    logger.debug(
+                        "Added series to database: %s (key=%s)",
+                        serie.name,
+                        serie.key
+                    )
+            # Commit happens automatically via get_db_session context
+            logger.info(
+                "Synced %d new series to database (skipped %d existing)",
+                added_count,
+                len(all_series) - added_count
+            )
+            return added_count
+
+    except Exception as e:
+        logger.warning(
+            "Failed to sync series to database: %s",
+            e,
+            exc_info=True
+        )
+        return 0
+
+
 @asynccontextmanager
 async def lifespan(app: FastAPI):
     """Manage application lifespan (startup and shutdown)."""
@@ -104,6 +176,11 @@ async def lifespan(app: FastAPI):
                 download_service = get_download_service()
                 await download_service.initialize()
                 logger.info("Download service initialized and queue restored")
+                
+                # Sync series from data files to database
+                await _sync_series_to_database(
+                    settings.anime_directory, logger
+                )
             else:
                 logger.info(
                     "Download service initialization skipped - "