Refactor CI to use common-ci-configuration templates

- Replace pre_get_sources hook with .haf_git_corruption_cleanup reference
  plus project-specific nested submodule cleanup
- Extend .haf_commit_validation for validate_haf_commit job
- Use .haf_app_sync_setup, .fetch_cache_manager, .haf_app_fetch_haf_cache
  references in sync job before_script
- Extend .haf_app_sync_variables for common directory variables
- Add global variable aliases (APP_SYNC_CACHE_TYPE, APP_CACHE_KEY,
  HAF_APP_SCHEMA) for common template compatibility
- Update skip_rules.yml documentation

Net reduction of ~99 lines while maintaining all functionality.