docs: figma-patterns - Say how to register a new pattern file on Studio #4040

Found in scaffold end-to-end test run 2 (10 Nov 2026, step 3d, finding P4).

Problem

After Pattern mode writes a new patterns/*.php file, WordPress keeps using its cached list of theme pattern files. studio wp cache flush and studio wp transient delete --all don't clear that cache, so the new pattern isn't registered, and a page that uses it renders nothing. Nothing in the skill says so.

Fix

In figma-to-block-theme/references/studio-operations.md (and the Pattern mode verify step), say: after adding or renaming a pattern file, run studio wp eval 'wp_get_theme()->delete_pattern_cache();', or set WP_DEVELOPMENT_MODE to theme while building. Check registration with WP_Block_Patterns_Registry::get_instance()->get_registered( '<slug>' ).

Done when

The skill's verify step registers a new pattern without guesswork.