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/rss/tests/parser_tests.rs

@@ -1,5 +1,5 @@
 use domain::Value;
-use rss_adapter::{parse_rss, RssError};
+use rss_adapter::{RssError, parse_rss};
 
 const SAMPLE_RSS: &str = r#"<?xml version="1.0" encoding="UTF-8"?>
     <rss version="2.0">
@@ -23,8 +23,20 @@ const SAMPLE_RSS: &str = r#"<?xml version="1.0" encoding="UTF-8"?>
 fn parses_rss_into_value() {
     let result = parse_rss(SAMPLE_RSS).unwrap();
 
-    assert_eq!(result.get_path("$.title"), Some(&Value::String("Test Feed".into())));
-    assert_eq!(result.get_path("$.items[0].title"), Some(&Value::String("First Article".into())));
-    assert_eq!(result.get_path("$.items[1].title"), Some(&Value::String("Second Article".into())));
-    assert_eq!(result.get_path("$.items[0].description"), Some(&Value::String("Description of first article".into())));
+    assert_eq!(
+        result.get_path("$.title"),
+        Some(&Value::String("Test Feed".into()))
+    );
+    assert_eq!(
+        result.get_path("$.items[0].title"),
+        Some(&Value::String("First Article".into()))
+    );
+    assert_eq!(
+        result.get_path("$.items[1].title"),
+        Some(&Value::String("Second Article".into()))
+    );
+    assert_eq!(
+        result.get_path("$.items[0].description"),
+        Some(&Value::String("Description of first article".into()))
+    );
 }