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/http-json/src/lib.rs

@@ -14,26 +14,32 @@ pub enum HttpJsonError {
     Parse(String),
 }
 
-impl HttpJsonAdapter {
-    pub fn new() -> Self {
+impl Default for HttpJsonAdapter {
+    fn default() -> Self {
         Self {
             client: reqwest::Client::new(),
         }
     }
 }
 
+impl HttpJsonAdapter {
+    pub fn new() -> Self {
+        Self::default()
+    }
+}
+
 fn json_to_value(json: serde_json::Value) -> Value {
     match json {
         serde_json::Value::Null => Value::Null,
         serde_json::Value::Bool(b) => Value::Bool(b),
         serde_json::Value::Number(n) => Value::Number(n.as_f64().unwrap_or(0.0)),
         serde_json::Value::String(s) => Value::String(s),
-        serde_json::Value::Array(arr) => {
-            Value::Array(arr.into_iter().map(json_to_value).collect())
-        }
-        serde_json::Value::Object(map) => {
-            Value::Object(map.into_iter().map(|(k, v)| (k, json_to_value(v))).collect())
-        }
+        serde_json::Value::Array(arr) => Value::Array(arr.into_iter().map(json_to_value).collect()),
+        serde_json::Value::Object(map) => Value::Object(
+            map.into_iter()
+                .map(|(k, v)| (k, json_to_value(v)))
+                .collect(),
+        ),
     }
 }