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/tests/environment.md

@@ -0,0 +1,71 @@
+# Test Environment
+
+## Runtime Requirements
+
+| Requirement | Specification |
+|-------------|--------------|
+| Python | 3.10+ |
+| OS | Linux or macOS (POSIX filesystem paths) |
+| GPU | Optional — ONNX inference falls back to CPUExecutionProvider |
+| Disk | Temp directory for fixture data (~500MB for augmentation output) |
+| Network | Not required (all tests are offline) |
+
+## Execution Modes
+
+Tests MUST be runnable in two ways:
+
+### 1. Local (no Docker) — primary mode
+Run directly on the host machine. Required for macOS development where Docker has GPU/performance limitations.
+
+```bash
+scripts/run-tests-local.sh
+```
+
+### 2. Docker — CI/portable mode
+Run inside a container for reproducible CI environments (Linux-based CI runners).
+
+```bash
+docker compose -f docker-compose.test.yml up --build --abort-on-container-exit
+```
+
+Both modes run the same pytest suite; the only difference is the runtime environment.
+
+## Dependencies
+
+All test dependencies are a subset of the production `requirements.txt` plus pytest:
+
+| Package | Purpose |
+|---------|---------|
+| pytest | Test runner |
+| albumentations | Augmentation tests |
+| opencv-python-headless | Image I/O (headless — no GUI) |
+| numpy | Array operations |
+| onnxruntime | ONNX inference (CPU fallback) |
+| cryptography | Encryption tests |
+| msgpack | Annotation queue message tests |
+| PyYAML | Config/YAML generation tests |
+
+## Fixture Data
+
+| Fixture | Location | Size |
+|---------|----------|------|
+| 100 annotated images | `_docs/00_problem/input_data/dataset/images/` | ~50MB |
+| 100 YOLO labels | `_docs/00_problem/input_data/dataset/labels/` | ~10KB |
+| ONNX model | `_docs/00_problem/input_data/azaion.onnx` | 81MB |
+| Class definitions | `classes.json` (project root) | 2KB |
+
+## Test Isolation
+
+- Each test creates a temporary directory (via `tmp_path` pytest fixture) for filesystem operations
+- No tests modify the actual `/azaion/` directory structure
+- No tests require running external services (RabbitMQ, Azaion API, S3 CDN)
+- Constants paths are patched/overridden to point to temp directories during tests
+
+## Excluded (Require External Services)
+
+| Component | Service Required | Reason for Exclusion |
+|-----------|-----------------|---------------------|
+| API upload/download | Azaion REST API | No mock server; real API has auth |
+| CDN upload/download | S3-compatible CDN | No mock S3; real CDN has credentials |
+| Queue consumption | RabbitMQ Streams | No mock broker; rstream requires live connection |
+| TensorRT inference | NVIDIA GPU + TensorRT | Hardware-specific; cannot run in CI without GPU |