Improve Bricks CSS regen and styling docs
Add clear guidance to prefer global classes over per-element inline styles and document CSS compilation behavior across MCP tools (bricks-builder-mcp.php and class-tool-site.php). Update Tool_Cache: expand tool description text and rework regenerate_css to prefer Bricks\Assets_Files::regenerate_css_files, handle optional post_id via generate_post_css_file, fallback to Bricks\CSS_Files for per-post generation, and finally to Bricks\Breakpoints as a last resort. Return more detailed status info and error messages. Also adjust a comment in cache clearing. These changes improve reliability of programmatic styling workflows and give clearer instructions for when to call bricks_regenerate_css and bricks_clear_cache.