internal data sources (clock, static text), connection indicator, rendering fixes

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.

crates/adapters/media/src/lib.rs

@@ -38,11 +38,19 @@ impl DataSourcePort for MediaAdapter {
     type Error = MediaError;
 
     async fn poll(&self, source: &DataSource) -> Result<Value, Self::Error> {
-        let base_url = source.config.url.as_ref().ok_or(MediaError::NoUrl)?;
-        let username = find_header(&source.config.headers, "username")
-            .ok_or(MediaError::MissingField("username"))?;
-        let password = find_header(&source.config.headers, "password")
-            .ok_or(MediaError::MissingField("password"))?;
+        let domain::DataSourceConfig::External {
+            ref url,
+            ref headers,
+            ..
+        } = source.config
+        else {
+            return Err(MediaError::NoUrl);
+        };
+        let base_url = url.as_ref().ok_or(MediaError::NoUrl)?;
+        let username =
+            find_header(headers, "username").ok_or(MediaError::MissingField("username"))?;
+        let password =
+            find_header(headers, "password").ok_or(MediaError::MissingField("password"))?;
 
         let salt: String = (0..12).map(|_| fastrand::alphanumeric()).collect();
         let token = subsonic_token(password, &salt);

crates/adapters/media/tests/media_tests.rs

@@ -45,7 +45,7 @@ fn make_source(url: String) -> DataSource {
         name: "navidrome".into(),
         source_type: DataSourceType::Media,
         poll_interval: Duration::from_secs(5),
-        config: DataSourceConfig {
+        config: DataSourceConfig::External {
             url: Some(url),
             headers: vec![
                 ("username".into(), "test".into()),