add config-sqlite and http-api adapters

SQLite config store: full ConfigRepository impl with JSON serialization
for mappings, layouts, data source configs. 12 integration tests.

HTTP API: Axum REST endpoints for widgets, data sources, layout, presets.
6 integration tests using tower::oneshot.

Port traits updated to return Send futures for Axum compatibility.

crates/domain/src/ports/broadcast.rs

@@ -1,17 +1,18 @@
+use std::future::Future;
 use crate::entities::WidgetId;
 use crate::value_objects::{Layout, WidgetState};
 
 pub trait BroadcastPort {
     type Error;
 
-    async fn push_screen_update(
+    fn push_screen_update(
         &self,
         layout: &Layout,
         widgets: &[(WidgetId, WidgetState)],
-    ) -> Result<(), Self::Error>;
+    ) -> impl Future<Output = Result<(), Self::Error>> + Send;
 
-    async fn push_data_update(
+    fn push_data_update(
         &self,
         updates: &[(WidgetId, WidgetState)],
-    ) -> Result<(), Self::Error>;
+    ) -> impl Future<Output = Result<(), Self::Error>> + Send;
 }