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.

.cursor/skills/refactor/phases/06-test-sync.md

@@ -0,0 +1,51 @@
+# Phase 6: Test Synchronization
+
+**Role**: QA engineer and developer
+**Goal**: Reconcile the test suite with the refactored codebase — remove obsolete tests, update broken tests, add tests for new code
+**Constraints**: All tests must pass at the end of this phase. Do not change production code here — only tests.
+
+## 6a. Identify Obsolete Tests
+
+1. Compare the pre-refactoring codebase structure (from Phase 0 inventory) with the current state
+2. Find tests that reference removed functions, classes, modules, or endpoints
+3. Find tests that duplicate coverage due to merged/consolidated code
+4. Decide per test: **delete** (functionality removed) or **merge** (duplicates)
+
+Write `REFACTOR_DIR/test_sync/obsolete_tests.md`:
+- Test file, test name, reason (target removed / target merged / duplicate coverage), action taken (deleted / merged into)
+
+## 6b. Update Existing Tests
+
+1. Run the full test suite — collect failures and errors
+2. For each failing test, determine the cause:
+   - Renamed/moved function or module → update import paths and references
+   - Changed function signature → update call sites and assertions
+   - Changed behavior (intentional per refactoring plan) → update expected values
+   - Changed data structures → update fixtures and assertions
+3. Fix each test, re-run to confirm it passes
+
+Write `REFACTOR_DIR/test_sync/updated_tests.md`:
+- Test file, test name, change type (import path / signature / assertion / fixture), description of update
+
+## 6c. Add New Tests
+
+1. Identify new code introduced during Phases 4–5 that lacks test coverage:
+   - New public functions, classes, or modules
+   - New interfaces or abstractions introduced during decoupling
+   - New error handling paths
+2. Write tests following the same patterns and conventions as the existing test suite
+3. Ensure coverage targets from Phase 3 are maintained or improved
+
+Write `REFACTOR_DIR/test_sync/new_tests.md`:
+- Test file, test name, target function/module, coverage type (unit / integration / blackbox)
+
+**Self-verification**:
+- [ ] All obsolete tests removed or merged
+- [ ] All pre-existing tests pass after updates
+- [ ] New code from Phases 4–5 has test coverage
+- [ ] Overall coverage meets or exceeds Phase 3 baseline (75% overall, 90% critical paths)
+- [ ] No tests reference removed or renamed code
+
+**Save action**: Write test_sync artifacts; implemented tests go into the project's test folder
+
+**GATE (BLOCKING)**: ALL tests must pass before proceeding to Phase 7. If tests fail, fix the tests or ask user for guidance.