Fix import error: Use relative imports for services modules

backend/main.py

@@ -13,10 +13,10 @@ import shutil
 from pathlib import Path
 import json
 
-from services.stem_separation import StemSeparationService
-from services.midi_extraction import MIDIExtractionService
-from services.audio_analysis import AudioAnalysisService
-from services.music_generation import MusicGenerationService, MusicPrompt
+from .services.stem_separation import StemSeparationService
+from .services.midi_extraction import MIDIExtractionService
+from .services.audio_analysis import AudioAnalysisService
+from .services.music_generation import MusicGenerationService, MusicPrompt
 from dotenv import load_dotenv
 
 load_dotenv()