feat(clean-release): complete and verify backend test suite (33 passing tests)

- Relocated and standardized tests for clean_release subsystem into __tests__ sub-packages.
- Implemented missing unit tests for preparation_service, audit_service, and stages.
- Enhanced API contract tests for candidate preparation and compliance reporting.
- Updated 023-clean-repo-enterprise coverage matrix with final verification results.
- Fixed relative import issues and model validation mismatches during test migration.

frontend/src/components/__tests__/task_log_viewer.test.js

@@ -1,5 +1,5 @@
 // [DEF:frontend.src.components.__tests__.task_log_viewer:Module]
-// @TIER: CRITICAL
+// @TIER: STANDARD
 // @SEMANTICS: tests, task-log, viewer, mount, components
 // @PURPOSE: Unit tests for TaskLogViewer component by mounting it and observing the DOM.
 // @LAYER: UI (Tests)