* refactor(storage): remove chat rooms and agent loops
This is the prerequisite cleanup for the storage backend migration. Legacy wire schemas remain temporarily so mixed-version peers can still parse old messages, while daemon callers now use query-shaped AgentStorage methods that can map directly to SQL later.
* test(cli): remove retired chat and loop coverage
* Rework docs navigation and move alternatives to top-level pages
- Add nested docs nav with categories, collapsible groups, breadcrumbs,
and a right-hand page outline with heading slugs.
- Move alternatives out of /docs/alternatives into /alternatives/*
marketing pages with 301 redirects.
- Add github-slugger for heading IDs and require explicit width on
SiteShell so new pages can't accidentally pick the narrow prose layout.
- Remove the best-practices doc from public-docs.
* Make docs content column prose-width
