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/http-api/src/lib.rs

@@ -1,9 +1,9 @@
 mod routes;
 
-use std::sync::Arc;
 use axum::Router;
-use tower_http::cors::CorsLayer;
 use domain::{ConfigRepository, EventPublisher};
+use std::sync::Arc;
+use tower_http::cors::CorsLayer;
 
 pub struct AppState<C, E> {
     pub config: Arc<C>,