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/bootstrap/src/main.rs

@@ -1,14 +1,15 @@
 mod config;
+mod event_handler;
 mod polling;
 
-use std::sync::Arc;
 use anyhow::Result;
 use application::DataProjection;
 use config_sqlite::SqliteConfigStore;
-use tcp_server::{TcpBroadcaster, TcpEventBus, run_tcp_server};
 use http_api::AppState;
+use std::sync::Arc;
+use tcp_server::{TcpBroadcaster, TcpEventBus, run_tcp_server};
 use tokio::sync::Mutex;
-use tracing::{info, error};
+use tracing::{error, info};
 
 #[tokio::main]
 async fn main() -> Result<()> {
@@ -53,5 +54,19 @@ async fn main() -> Result<()> {
 
     info!("K-Frame server running");
 
-    polling::run(config_store, broadcaster, projection, cfg.poll_interval_secs).await
+    let ev_bus = event_bus.clone();
+    let ev_config = config_store.clone();
+    let ev_bc = broadcaster.clone();
+    let ev_proj = projection.clone();
+    tokio::spawn(async move {
+        event_handler::run(ev_bus, ev_config, ev_bc, ev_proj).await;
+    });
+
+    polling::run(
+        config_store,
+        broadcaster,
+        projection,
+        cfg.poll_interval_secs,
+    )
+    .await
 }