docs: update roadmap to reflect Phase 3 completion

Mark Phase 3 (Reusable YAML Blocks) as completed with table of
implemented templates including:
- .fetch_cache_manager
- .haf_app_wait_for_postgres
- .haf_app_wait_for_postgrest (with DNS fix)
- .cleanup_stale_cache
- .cleanup_cache_manual_template
- .cleanup_old_cache_template