fix async handling in SerieScanner and add image_downloader cleanup

- SerieScanner.scan() now detects running event loop and uses create_task()
  when already in async context, avoids RuntimeError
- NFOService.close() now also closes image_downloader to prevent resource leaks
- Add integration tests for TMDBClient lifecycle management

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/core/SerieScanner.py

@@ -44,8 +44,13 @@ class SerieScanner:
         in keyDict and can be retrieved after scanning.
     
     Example:
+        # Synchronous context (CLI):
         scanner = SerieScanner("/path/to/anime", loader)
-        scanner.scan()
+        scanner.scan()  # asyncio.run() used internally when no event loop
+
+        # Asynchronous context (server/scheduler):
+        # scan() detects running event loop and uses create_task()
+        # internally, so no special handling needed by caller.
         # Results are in scanner.keyDict
 
         # With DB lookup fallback:
@@ -432,7 +437,14 @@ class SerieScanner:
 
                         # Persist to database (async)
                         try:
-                            asyncio.run(self._persist_serie_to_db(serie))
+                            try:
+                                loop = asyncio.get_running_loop()
+                            except RuntimeError:
+                                # No running loop — safe to use asyncio.run()
+                                asyncio.run(self._persist_serie_to_db(serie))
+                            else:
+                                # Already in async context — schedule as task
+                                asyncio.create_task(self._persist_serie_to_db(serie))
                         except Exception as e:
                             logger.warning(
                                 "DB persistence failed for '%s', "