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/client-domain/src/lib.rs

@@ -1,9 +1,9 @@
 mod bounding_box;
 mod layout_engine;
-mod render_tree;
 pub mod ports;
+mod render_tree;
 
 pub use bounding_box::BoundingBox;
 pub use layout_engine::LayoutEngine;
+pub use ports::{ClientConfig, DisplayPort, NetworkPort, StoragePort};
 pub use render_tree::RenderTree;
-pub use ports::{DisplayPort, NetworkPort, StoragePort, ClientConfig};