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)

Cargo.lock

@@ -166,6 +166,8 @@ dependencies = [
  "dotenvy",
  "http-api",
  "http-json",
+ "media-adapter",
+ "rss-adapter",
  "tcp-server",
  "tokio",
  "tracing",
@@ -1102,12 +1104,20 @@ dependencies = [
  "digest",
 ]
 
+[[package]]
+name = "md5"
+version = "0.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "490cc448043f947bae3cbee9c203358d62dbee0db12107a74be5c30ccfd09771"
+
 [[package]]
 name = "media-adapter"
 version = "0.1.0"
 dependencies = [
  "axum",
  "domain",
+ "fastrand",
+ "md5",
  "reqwest",
  "serde_json",
  "thiserror",