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_tasks/AZ-160_test_hardware_hash.md

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+# Hardware Hash & API Key Tests
+
+**Task**: AZ-160_test_hardware_hash
+**Name**: Hardware Hash & API Key Tests
+**Description**: Implement 7 tests for hardware fingerprinting — determinism, uniqueness, base64 format, API key derivation from credentials and hardware
+**Complexity**: 2 points
+**Dependencies**: AZ-152_test_infrastructure
+**Component**: Blackbox Tests
+**Jira**: AZ-160
+**Epic**: AZ-151
+
+## Problem
+
+Hardware hashing provides machine-bound security for model encryption and API authentication. Tests must verify determinism, uniqueness, format, and credential/hardware dependency.
+
+## Outcome
+
+- 7 passing pytest tests in `tests/test_hardware_hash.py`
+
+## Scope
+
+### Included
+- BT-HSH-01: Deterministic output (same input → same hash)
+- BT-HSH-02: Different inputs → different hashes
+- BT-HSH-03: Output is valid base64
+- ST-HSH-01: Hardware hash deterministic (duplicate of BT-HSH-01 for security coverage)
+- ST-HSH-02: Different hardware → different hash
+- ST-HSH-03: API encryption key depends on credentials + hardware
+- ST-HSH-04: API encryption key depends on credentials
+
+### Excluded
+- Actual hardware info collection (may need mocking)
+
+## Acceptance Criteria
+
+**AC-1: Determinism**
+Given "test-hardware-info"
+When get_hw_hash() called twice
+Then both calls return identical string
+
+**AC-2: Uniqueness**
+Given "hw-a" and "hw-b"
+When get_hw_hash() called on each
+Then results differ
+
+**AC-3: Base64 format**
+Given "test-hardware-info"
+When get_hw_hash() called
+Then result matches `^[A-Za-z0-9+/]+=*$`
+
+**AC-4: API key depends on hardware**
+Given same credentials, different hardware hashes
+When get_api_encryption_key() called
+Then different keys returned
+
+**AC-5: API key depends on credentials**
+Given different credentials, same hardware hash
+When get_api_encryption_key() called
+Then different keys returned
+
+## Constraints
+
+- Security tests marked: `@pytest.mark.security`
+- May require mocking hardware info collection functions
+- All inputs are generated strings (no external fixtures)