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/exports.md

@@ -0,0 +1,53 @@
+# Module: exports
+
+## Purpose
+Model export utilities: converts trained YOLO .pt models to ONNX, TensorRT, and RKNN formats. Also handles encrypted model upload (split big/small pattern) and data sampling.
+
+## Public Interface
+
+| Function | Signature | Returns | Description |
+|----------|-----------|---------|-------------|
+| `export_rknn` | `(model_path: str)` | — | Exports YOLO model to RKNN format (RK3588 target), cleans up temp folder |
+| `export_onnx` | `(model_path: str, batch_size: int = 4)` | — | Exports YOLO model to ONNX (1280px, NMS enabled, GPU device 0) |
+| `export_tensorrt` | `(model_path: str)` | — | Exports YOLO model to TensorRT engine (batch=4, half precision, NMS) |
+| `form_data_sample` | `(destination_path: str, size: int = 500, write_txt_log: bool = False)` | — | Creates a random sample of processed images |
+| `show_model` | `(model: str = None)` | — | Opens model visualization in netron |
+| `upload_model` | `(model_path: str, filename: str, size_small_in_kb: int = 3)` | — | Encrypts model, splits big/small, uploads to API + CDN |
+
+## Internal Logic
+- **export_onnx**: Removes existing ONNX file if present, exports at 1280px with NMS baked in and simplification.
+- **export_tensorrt**: Uses YOLO's built-in TensorRT export (batch=4, FP16, NMS, simplify).
+- **export_rknn**: Exports to RKNN format targeting RK3588 SoC, moves result file and cleans temp directory.
+- **upload_model**: Encrypts with `Security.get_model_encryption_key()`, splits encrypted bytes at 30%/70% boundary (or `size_small_in_kb * 1024`), uploads small part to API, big part to CDN.
+- **form_data_sample**: Randomly shuffles processed images, copies first N to destination folder.
+
+## Dependencies
+- `constants` — directory paths, model paths, config file names
+- `api_client` — ApiClient, ApiCredentials for upload
+- `cdn_manager` — CDNManager, CDNCredentials for CDN upload
+- `security` — model encryption key, encrypt_to
+- `utils` — Dotdict for config access
+- `ultralytics` (external) — YOLO model
+- `netron` (external) — model visualization
+- `yaml`, `os`, `shutil`, `random`, `pathlib` (stdlib)
+
+## Consumers
+train (export_tensorrt, upload_model, export_onnx)
+
+## Data Models
+None.
+
+## Configuration
+Reads `config.yaml` for API credentials (in `upload_model`), `cdn.yaml` for CDN credentials.
+
+## External Integrations
+- Ultralytics YOLO export pipeline
+- Netron model viewer
+- Azaion API + CDN for model upload
+
+## Security
+- Models are encrypted with AES-256-CBC before upload
+- Split storage (big on CDN, small on API) prevents single-point compromise
+
+## Tests
+None.