feat: add full API schema caching to YAML catalog

- Extend RouteInfo with DataColumn, Frequency dataclasses and API-fetched
  fields (data_columns, frequencies, start/end_period, api_hash)
- refresh() now fetches full metadata + all facet values per route in
  parallel (ThreadPoolExecutor), with SHA-256 hash-based change detection
- get_data_endpoint() uses cached catalog schema to skip API metadata call
- FacetInfo.get_values() returns cached values when available (no API call)
- FacetHint gains `values` field for full API-fetched facet options
- Update skill to Python-first approach (scripts default, CLI for quick lookups)
- Migrate source to src/ layout, add tests and catalog_manager module

Author: jsulopzs