refactor: consolidate counting config through src/config_loader

- config.yaml gains counting.max_reid_frames (200) + debounce_frames (8);
  CountingConfig + parsing + pinned-value test added
- predict.py load_zones() delegates to read_zone_polygons() (geometry only);
  legacy zones.json knob reads removed (config.yaml is canonical)
- run_prediction wires 5 more live knobs from cfg.counting.* (entry/exit
  overlap, tolerance_missing_frames, max_reid_frames, debounce_frames)
- delete deprecated src/config.py (v3 keys) + tests/test_config.py;
  src/main.py bridges onto unified config so the deprecated entrypoint
  keeps working
- 8 never-read globals (JARAK_ABSORBSI_GHOST, CAMERA_NOISE_DEADBAND, ...)
  left untouched — flagged for Phase 2 dead-code cleanup

Verified: pytest 21 passed; full pipeline runs on synthetic video
(engines load, 30 frames, clean finish).

config.yaml

@@ -112,6 +112,8 @@ counting:
   circle_stay_timeout_sec: 10.0
   jarak_toleransi_duplikat: 30
   tolerance_missing_frames: 1200
+  max_reid_frames: 200
+  debounce_frames: 8
 
 batch:
   timeout_seconds: 30.0