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/hardware_service.md

@@ -0,0 +1,38 @@
+# Module: hardware_service
+
+## Purpose
+Collects hardware fingerprint information (CPU, GPU, RAM, drive serial) from the host machine for use in hardware-bound encryption key derivation.
+
+## Public Interface
+
+| Function | Signature | Returns |
+|----------|-----------|---------|
+| `get_hardware_info` | `() -> str` | Formatted string: `CPU: {cpu}. GPU: {gpu}. Memory: {memory}. DriveSerial: {drive_serial}` |
+
+## Internal Logic
+- Detects OS via `os.name` (`nt` for Windows, else Linux)
+- **Windows**: PowerShell commands to query `Win32_Processor`, `Win32_VideoController`, `Win32_OperatingSystem`, disk serial
+- **Linux**: `lscpu`, `lspci`, `free`, `/sys/block/sda/device/` serial
+- Parses multi-line output: first line = CPU, second = GPU, second-to-last = memory, last = drive serial
+- Handles multiple GPUs by taking first GPU and last two lines for memory/drive
+
+## Dependencies
+- `os`, `subprocess` (stdlib)
+
+## Consumers
+api_client (used in `load_bytes` to generate hardware string for encryption)
+
+## Data Models
+None.
+
+## Configuration
+None.
+
+## External Integrations
+Executes OS-level shell commands to query hardware.
+
+## Security
+The hardware fingerprint is used as input to `Security.get_hw_hash()` and subsequently `Security.get_api_encryption_key()`, binding API encryption to the specific machine.
+
+## Tests
+None.