Refactor constants management to use Pydantic BaseModel for configuration

- Replaced module-level path variables in constants.py with a structured Pydantic Config class.
- Updated all relevant modules (train.py, augmentation.py, exports.py, dataset-visualiser.py, manual_run.py) to access paths through the new config structure.
- Fixed bugs related to image processing and model saving.
- Enhanced test infrastructure to accommodate the new configuration approach.

This refactor improves code maintainability and clarity by centralizing configuration management.

_docs/02_document/modules/dto_imageLabel.md

@@ -0,0 +1,41 @@
+# Module: dto/imageLabel
+
+## Purpose
+Container class for an image with its YOLO-format bounding box labels, plus a visualization method for debugging annotations.
+
+## Public Interface
+
+### ImageLabel
+| Field/Method | Type/Signature | Description |
+|-------------|----------------|-------------|
+| `image_path` | str | Filesystem path to the image |
+| `image` | numpy.ndarray | OpenCV image array |
+| `labels_path` | str | Filesystem path to the labels file |
+| `labels` | list[list] | List of YOLO bboxes: [x_center, y_center, width, height, class_id] |
+| `visualize` | `(annotation_classes: dict) -> None` | Draws bounding boxes on image and displays via matplotlib |
+
+## Internal Logic
+- `visualize()` converts BGR→RGB, iterates labels, converts normalized YOLO coordinates to pixel coordinates, draws colored rectangles using `annotation_classes[class_num].color_tuple`, displays with matplotlib.
+- Labels use YOLO format: center_x, center_y, width, height (all normalized 0–1), class_id as last element.
+
+## Dependencies
+- `cv2` (external) — image manipulation
+- `matplotlib.pyplot` (external) — image display
+
+## Consumers
+augmentation (as augmented image container), dataset-visualiser (for visualization)
+
+## Data Models
+`ImageLabel` — image + labels container.
+
+## Configuration
+None.
+
+## External Integrations
+None.
+
+## Security
+None.
+
+## Tests
+Used by `tests/imagelabel_visualize_test.py`.