Centralize configuration into config.yaml

- All settings moved to config.yaml
- configs/load.py reads from config.yaml with env var overrides
- Environment variables still work for backward compatibility
- Added pyyaml to requirements

app/webrtc/video_receiver.py

@@ -10,7 +10,7 @@ from loguru import logger
 from app.audio.rep_announcer import RepAnnouncer
 from app.exercises.dead_bug.detector import DeadBugDetector
 from app.rendering.window_display import close_window, is_esc_pressed, show_frame
-from configs.default import (
+from configs.load import (
     EXTENSION_CONFIRM_FRAMES,
     MODEL_PATH,
     PREFER_GPU,