add SPA config UI, wire media/rss adapters, event-driven layout push

- React SPA: dashboard, data sources CRUD, widgets CRUD, layout builder,
  presets. TanStack Router + Query, shadcn/ui, Vite proxy to :3000
- wire media + rss adapters into polling loop, remove xtb source type
- media adapter: read username/password from headers, proper subsonic auth
- event handler: subscribe to LayoutChanged, push screen update to clients
- fix clippy warnings across workspace (Default impls, collapsible ifs,
  redundant closures, is_none_or, unused imports)

crates/adapters/tcp-server/src/lib.rs

@@ -1,9 +1,9 @@
-mod error;
 mod broadcaster;
+mod error;
 mod event_bus;
 mod server;
 
-pub use error::TcpServerError;
 pub use broadcaster::TcpBroadcaster;
+pub use error::TcpServerError;
 pub use event_bus::TcpEventBus;
 pub use server::run_tcp_server;