per-source polling, initial client state, webhook, preview, client tracking

- per-source poll intervals: spawn task per source with own interval,
  manager re-checks sources every 30s for add/remove
- initial screen update on TCP connect: send layout + widget states
- client tracking: ClientRegistry port, GET /api/clients, dashboard list
- webhook adapter: POST /api/webhook/{source_id} feeds data into projection
- widget preview: GET /api/widgets/{id}/preview returns current state
- serve SPA from Axum: ServeDir + index.html fallback via KFRAME_SPA_DIR
- layout builder delete confirmation with AlertDialog
- form validation: required fields disable save button
- guide page at /guide
- fix architecture: ClientDto to api-types, ClientRegistry + WidgetStateReader
  ports in domain, DataProjection has internal Mutex, no adapter cross-deps
- ESP32: full screen clear on layout change (stale pixel fix)

crates/domain/src/lib.rs

@@ -10,7 +10,10 @@ pub use entities::{
     LayoutPreset, LayoutPresetId, WidgetConfig, WidgetId,
 };
 pub use events::DomainEvent;
-pub use ports::{BroadcastPort, ConfigRepository, DataSourcePort, EventPublisher};
+pub use ports::{
+    BroadcastPort, ClientRegistry, ConfigRepository, ConnectedClient, DataSourcePort,
+    EventPublisher, WidgetStateReader,
+};
 pub use value_objects::{
     ContainerNode, Direction, DisplayHint, KeyMapping, Layout, LayoutChild, LayoutNode,
     LayoutValidationError, Sizing, Value, WidgetError, WidgetState,

crates/domain/src/ports/client_registry.rs

@@ -0,0 +1,11 @@
+#[derive(Clone)]
+pub struct ConnectedClient {
+    pub addr: String,
+    pub connected_at: u64,
+}
+
+pub trait ClientRegistry {
+    fn add_client(&self, addr: &str, connected_at: u64);
+    fn remove_client(&self, addr: &str);
+    fn list_clients(&self) -> Vec<ConnectedClient>;
+}

crates/domain/src/ports/mod.rs

@@ -1,9 +1,13 @@
 mod broadcast;
+mod client_registry;
 mod config_repository;
 mod data_source_port;
 mod event;
+mod widget_state_reader;
 
 pub use broadcast::BroadcastPort;
+pub use client_registry::{ClientRegistry, ConnectedClient};
 pub use config_repository::ConfigRepository;
 pub use data_source_port::DataSourcePort;
 pub use event::EventPublisher;
+pub use widget_state_reader::WidgetStateReader;

crates/domain/src/ports/widget_state_reader.rs

@@ -0,0 +1,14 @@
+use crate::entities::WidgetId;
+use crate::value_objects::WidgetState;
+use std::future::Future;
+
+pub trait WidgetStateReader {
+    fn get_widget_state(&self, id: WidgetId) -> impl Future<Output = Option<WidgetState>> + Send;
+
+    fn apply_raw_data(
+        &self,
+        source_id: u16,
+        raw: &crate::value_objects::Value,
+        widgets: &[crate::entities::WidgetConfig],
+    ) -> impl Future<Output = Vec<(WidgetId, WidgetState)>> + Send;
+}