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/application/src/data_projection.rs

@@ -1,15 +1,18 @@
-use std::collections::HashMap;
 use domain::{DataSourceId, Value, WidgetConfig, WidgetId, WidgetState};
+use std::collections::HashMap;
 
+#[derive(Default)]
 pub struct DataProjection {
     current: HashMap<WidgetId, WidgetState>,
 }
 
 impl DataProjection {
     pub fn new() -> Self {
-        Self {
-            current: HashMap::new(),
-        }
+        Self::default()
+    }
+
+    pub fn get_state(&self, widget_id: WidgetId) -> Option<&WidgetState> {
+        self.current.get(&widget_id)
     }
 
     pub fn apply_poll_result(
@@ -27,9 +30,10 @@ impl DataProjection {
 
             let new_state = config.extract(raw);
 
-            let is_changed = self.current
+            let is_changed = self
+                .current
                 .get(&config.id)
-                .map_or(true, |prev| *prev != new_state);
+                .is_none_or(|prev| *prev != new_state);
 
             if is_changed {
                 self.current.insert(config.id, new_state.clone());