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/media/Cargo.toml

@@ -8,6 +8,8 @@ domain.workspace = true
 reqwest.workspace = true
 serde_json.workspace = true
 thiserror.workspace = true
+md5 = "0.7"
+fastrand = "2"
 
 [dev-dependencies]
 tokio.workspace = true