rewire bootstrap with SQLite, HTTP API, and real polling

bootstrap: SQLite config, HTTP API on :3000, TCP on :2699, poll loops.
http-api: added serve() so bootstrap doesn't depend on axum directly.
polling: reads data sources from config, polls via http-json adapter,
pushes changed widgets to connected clients.

configure via API, e.g.:
  curl -X POST localhost:3000/api/data-sources -H 'Content-Type: application/json' -d '{...}'
  curl -X PUT localhost:3000/api/layout -H 'Content-Type: application/json' -d '{...}'

crates/adapters/http-api/Cargo.toml

@@ -11,6 +11,7 @@ axum.workspace = true
 tower-http.workspace = true
 serde.workspace = true
 serde_json.workspace = true
+tokio.workspace = true
 
 [dev-dependencies]
 tokio.workspace = true