feat: unified config.yaml with extensible model presets (A-D data-driven, E/F ready)

- config.yaml canonical for stream/models/counting/batch/output/camera
- models.modes hold engines+class filters only; conf/iou/min_bbox in detection_params
- predict.py derives tracker roles structurally (no per-mode branching)
- dashboard mode switch validates + persists atomically to config.yaml
- .env keeps secrets/deployment only; zones.json geometry; tracker.yaml hyperparams
- batch_mode.json keeps manual/auto batch mode; legacy model_mode ignored w/ warning
- src/detection+tracking gain iou param (default 0.7 = no behavior change)

.github/workflows/ci.yml

@@ -12,6 +12,6 @@ jobs:
       - uses: actions/setup-python@v5
         with:
           python-version: "3.10"
-      - run: pip install numpy python-dotenv pytest
+      - run: pip install numpy python-dotenv pytest pyyaml
       - run: python -m pytest tests/ -q
       - run: python -m compileall -q src/ counter_dashboard.py