v1.2.0 of flutter_themed

Theme switching for Flutter apps. Supports light, dark, and custom themes with optional persistence. Changelog excerpt: ### Added - ThemedApp.router— named constructor that wraps MaterialApp.router, enabling full compatibility with any RouterConfigimplementation (go_router, auto_route, etc.) - No dependency on any routing package — flutter_themeduses Flutter's native RouterConfiginterface ### Changed - Updated FAQ: ThemedAppnow supports both MaterialAppand MaterialApp.router