Replace per-entity pages (/roasters, /roasts, /bags, /brews, /gear,
/cafes, /cups) and detail pages with a single tabbed /data view and
a dedicated /add page for entity creation.
- Add /data route with tab-based navigation using Datastar
- Add /add route consolidating all create forms
- Remove per-entity page handlers and standalone templates
- Remove detail page routes, handlers, and templates
- Update ListNavigator to accept String paths for query-param URLs
- Update home page and timeline links to use new /data?type=X paths
- Update nav to reference /data instead of individual entity pages
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