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/08-documentation.md

@@ -0,0 +1,46 @@
+# Phase 8: Documentation Update
+
+**Role**: Technical writer
+**Goal**: Update existing `_docs/` artifacts to reflect all changes made during refactoring
+**Constraints**: Documentation only — no code changes. Only update docs that are affected by refactoring changes.
+
+**Skip condition**: If no `_docs/02_document/` directory exists (standalone mode), skip this phase entirely.
+
+## 8a. Identify Affected Documentation
+
+1. Review `REFACTOR_DIR/execution_log.md` to list all files changed during Phase 4
+2. Review any hardening changes from Phase 5
+3. Review test changes from Phase 6
+4. Map changed files to their corresponding module docs in `_docs/02_document/modules/`
+5. Map changed modules to their parent component docs in `_docs/02_document/components/`
+6. Determine if system-level docs need updates (`architecture.md`, `system-flows.md`, `data_model.md`)
+7. Determine if test documentation needs updates (`_docs/02_document/tests/`)
+
+## 8b. Update Module Documentation
+
+For each module doc affected by refactoring changes:
+1. Re-read the current source file
+2. Update the module doc to reflect new/changed interfaces, dependencies, internal logic
+3. Remove documentation for deleted code; add documentation for new code
+
+## 8c. Update Component Documentation
+
+For each component doc affected:
+1. Re-read the updated module docs within the component
+2. Update inter-module interfaces, dependency graphs, caveats
+3. Update the component relationship diagram if component boundaries changed
+
+## 8d. Update System-Level Documentation
+
+If structural changes were made (new modules, removed modules, changed interfaces):
+1. Update `_docs/02_document/architecture.md` if architecture changed
+2. Update `_docs/02_document/system-flows.md` if flow sequences changed
+3. Update `_docs/02_document/diagrams/components.md` if component relationships changed
+
+**Self-verification**:
+- [ ] Every changed source file has an up-to-date module doc
+- [ ] Component docs reflect the refactored structure
+- [ ] No stale references to removed code in any doc
+- [ ] Dependency graphs in docs match actual imports
+
+**Save action**: Updated docs written in-place to `_docs/02_document/`