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/protocol/src/lib.rs

@@ -1,13 +1,11 @@
-mod wire;
 mod frame;
+mod wire;
 
-pub use wire::{
-    WireValue, WireWidgetState, WireWidgetError, WireDisplayHint,
-    WireLayoutNode, WireContainerNode, WireLayoutChild, WireDirection, WireSizing,
-    WireKeyValue,
-};
 pub use frame::{
-    ServerMessage, ClientMessage, WidgetDescriptor,
-    encode, decode_server_message, encode_client, decode_client_message,
-    MAX_FRAME_SIZE,
+    ClientMessage, MAX_FRAME_SIZE, ServerMessage, WidgetDescriptor, decode_client_message,
+    decode_server_message, encode, encode_client,
+};
+pub use wire::{
+    WireContainerNode, WireDirection, WireDisplayHint, WireKeyValue, WireLayoutChild,
+    WireLayoutNode, WireSizing, WireValue, WireWidgetError, WireWidgetState,
 };