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/domain/tests/data_source_tests.rs

@@ -1,5 +1,5 @@
-use std::time::Duration;
 use domain::{DataSource, DataSourceConfig, DataSourceType, DataSourceValidationError};
+use std::time::Duration;
 
 fn make_source(source_type: DataSourceType, url: Option<&str>, poll: Duration) -> DataSource {
     DataSource {
@@ -38,14 +38,22 @@ fn webhook_with_zero_interval_is_valid() {
 
 #[test]
 fn poll_based_source_requires_nonzero_interval() {
-    let source = make_source(DataSourceType::Weather, Some("https://api.weather.com"), Duration::ZERO);
+    let source = make_source(
+        DataSourceType::Weather,
+        Some("https://api.weather.com"),
+        Duration::ZERO,
+    );
     let errors = source.validate();
     assert!(errors.contains(&DataSourceValidationError::PollIntervalRequired));
 }
 
 #[test]
 fn valid_poll_source_has_no_errors() {
-    let source = make_source(DataSourceType::Rss, Some("https://feed.example.com"), Duration::from_secs(300));
+    let source = make_source(
+        DataSourceType::Rss,
+        Some("https://feed.example.com"),
+        Duration::from_secs(300),
+    );
     let errors = source.validate();
     assert!(errors.is_empty());
 }