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 '{...}'

Cargo.toml

@@ -34,6 +34,7 @@ tcp-server = { path = "crates/adapters/tcp-server" }
 tcp-client = { path = "crates/adapters/tcp-client" }
 display-terminal = { path = "crates/adapters/display-terminal" }
 config-sqlite = { path = "crates/adapters/config-sqlite" }
+http-json = { path = "crates/adapters/http-json" }
 http-api = { path = "crates/adapters/http-api" }
 axum = { version = "0.8", features = ["macros"] }
 tower-http = { version = "0.6", features = ["cors"] }