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/tests/round_trip_tests.rs

@@ -1,8 +1,7 @@
 use protocol::{
-    ServerMessage, ClientMessage, WidgetDescriptor,
-    WireDisplayHint, WireLayoutNode, WireContainerNode, WireLayoutChild,
-    WireDirection, WireSizing, WireWidgetState, WireKeyValue, WireValue,
-    encode, decode_server_message, encode_client, decode_client_message,
+    ClientMessage, ServerMessage, WidgetDescriptor, WireContainerNode, WireDirection,
+    WireDisplayHint, WireKeyValue, WireLayoutChild, WireLayoutNode, WireSizing, WireValue,
+    WireWidgetState, decode_client_message, decode_server_message, encode, encode_client,
 };
 
 #[test]
@@ -23,19 +22,23 @@ fn screen_update_round_trips() {
                 },
             ],
         }),
-        widgets: vec![
-            WidgetDescriptor {
-                id: 1,
-                display_hint: WireDisplayHint::IconValue,
-                state: WireWidgetState {
-                    data: vec![
-                        WireKeyValue { key: "temperature".into(), value: WireValue::String("5.4°C".into()) },
-                        WireKeyValue { key: "icon".into(), value: WireValue::String("cloud_rain".into()) },
-                    ],
-                    error: None,
-                },
+        widgets: vec![WidgetDescriptor {
+            id: 1,
+            display_hint: WireDisplayHint::IconValue,
+            state: WireWidgetState {
+                data: vec![
+                    WireKeyValue {
+                        key: "temperature".into(),
+                        value: WireValue::String("5.4°C".into()),
+                    },
+                    WireKeyValue {
+                        key: "icon".into(),
+                        value: WireValue::String("cloud_rain".into()),
+                    },
+                ],
+                error: None,
             },
-        ],
+        }],
     };
 
     let frame = encode(&msg).unwrap();
@@ -47,18 +50,17 @@ fn screen_update_round_trips() {
 #[test]
 fn data_update_round_trips() {
     let msg = ServerMessage::DataUpdate {
-        widgets: vec![
-            WidgetDescriptor {
-                id: 3,
-                display_hint: WireDisplayHint::TextBlock,
-                state: WireWidgetState {
-                    data: vec![
-                        WireKeyValue { key: "body".into(), value: WireValue::String("Breaking news...".into()) },
-                    ],
-                    error: None,
-                },
+        widgets: vec![WidgetDescriptor {
+            id: 3,
+            display_hint: WireDisplayHint::TextBlock,
+            state: WireWidgetState {
+                data: vec![WireKeyValue {
+                    key: "body".into(),
+                    value: WireValue::String("Breaking news...".into()),
+                }],
+                error: None,
             },
-        ],
+        }],
     };
 
     let frame = encode(&msg).unwrap();