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/src/value_objects/value.rs

@@ -17,10 +17,7 @@ impl Value {
             Value::Number(_) => 8,
             Value::String(s) => s.len(),
             Value::Array(arr) => arr.iter().map(|v| v.estimated_size()).sum(),
-            Value::Object(map) => map
-                .iter()
-                .map(|(k, v)| k.len() + v.estimated_size())
-                .sum(),
+            Value::Object(map) => map.iter().map(|(k, v)| k.len() + v.estimated_size()).sum(),
         }
     }