antigravity minimal

Instructions only; the product keeps its own defaults. This setup used to be an empty settings document instead, because this harness shipped no instruction anywhere and there was nothing else for a minimal setup to carry. It carries one now, through the plugin surface -- the product's own reference says a plugin's rules are automatically ingested when it is enabled, and AGENTS.md under rules/ is the shape it recommends. An empty {} reads as configured and does nothing.