Kill the loading spinner with local-first data and reactive SQL

Local-first web architecture combines in-browser SQLite (via WebAssembly), reactive SQL queries, and a background sync engine to eliminate loading spinners and network latency. Using React, PowerSync, and Supabase, this hands-on walkthrough shows how to set up a cloud database with row-level security, configure sync rules that shape per-user data, and wire up a React frontend where writes go directly to local SQLite and sync asynchronously to the cloud. The reactive `useQuery` hook replaces `useEffect`+`fetch` patterns, and writes complete in milliseconds without awaiting server responses. The tradeoff: more upfront schema and sync configuration in exchange for native-feeling, offline-capable apps.