Add dnt build script to compile TypeScript for npm distribution.
Update publish workflow to publish to both JSR and npm using
GitHub Actions OIDC trusted publishing with provenance.

BREAKING CHANGE: valTownAdapter has been renamed to sqliteAdapter.
The adapter works with any SQLite driver using the execute({ sql, args })
pattern - not just Val Town. This includes Val Town, libSQL, and Turso.

Framework-agnostic storage implementations for AT Protocol OAuth:
- OAuthStorage interface with TTL support
- MemoryStorage for testing/development
- SQLiteStorage with adapter pattern for any SQLite driver
- Pre-built adapters: valTownAdapter, denoSqliteAdapter, betterSqlite3Adapter