Consolidate provider-specific category mapping into resolve_model_category(),
shared JSON request handling into execute_provider_json_request(), sidecar
path resolution into get_or_build_model_sidecar_info(), and progress
reporting into ProgressTracker. Update civitai/civarchive/common sources to
use the unified helpers. Add tests for the new utilities. Remove redundant
frontend wrapper methods from render_format_methods.js.
Dariusz L