Advanced Accordion block (rich inner blocks + deep-linking)

The current “FAQ” block only allows paragraphs, which kills real-world use. We need an Accordion block that accepts any inner blocks (containers, buttons, images, lists, forms), supports nested accordions, and ships with: Deep-linking: open panel via URL hash, update URL on toggle. Controls: single/multiple open, “open on load” (by index/ID), Collapse/Expand All. Performance: no CLS, optional lazy render of panel content. Design: icons left/right, heading levels, borders, spacing, presets. SEO: optional FAQ schema per item or whole block. This replaces the limited FAQ and unlocks real layout flexibility without custom code.