DataSourceConfig refactored to enum: External/Clock/StaticText. Clock
generates formatted time via chrono, static text emits configured string.
ESP32: connection status indicator (green/red dot bottom-right), per-widget
clear before redraw, RenderEvent enum for local + server messages.
Polling uses DataUpdate instead of ScreenUpdate to avoid wiping widget state.
Empty mappings passthrough raw source data for internal sources.
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 '{...}'
api-types: standalone crate with DTOs (widget, data source, layout, preset)
extracted from http-api. Shared between http-api and future SPA.
thiserror: replaced all manual Display impls with derive macros across
8 crates (config-sqlite, config-memory, tcp-server, tcp-client,
http-json, rss, media, application).
