refact (core): simplifies constants.py, removes redundancy, updates dependent code

web/backend/api/info.py

@@ -9,7 +9,7 @@ from backend.services.task_manager import task_manager
 # Import core functions
 from audio_splitter.ffmpeg import get_stream_info, get_container_format, get_audio_codec
 from audio_splitter.formats import determine_default_format
-from audio_splitter.constants import FORMAT_INFO
+from audio_splitter.constants import CONTAINER_NAMES
 from audio_splitter.defaults import DEFAULT_FORMAT
 
 router = APIRouter(prefix="/api", tags=["info"])
@@ -63,7 +63,7 @@ async def get_recommended_format(task_id: str):
         # Fallback if detection fails or format is unsupported
         if fmt is None:
             fmt = DEFAULT_FORMAT
-        if fmt not in FORMAT_INFO:
+        if fmt not in CONTAINER_NAMES:
             fmt = "mp3"  # ultimate fallback
 
         return {"format": fmt}