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/domain/src/entities/data_source.rs

@@ -9,13 +9,24 @@ pub enum DataSourceType {
     Rss,
     HttpJson,
     Webhook,
+    Clock,
+    StaticText,
 }
 
 #[derive(Debug, Clone)]
-pub struct DataSourceConfig {
-    pub url: Option<String>,
-    pub headers: Vec<(String, String)>,
-    pub api_key: Option<String>,
+pub enum DataSourceConfig {
+    External {
+        url: Option<String>,
+        headers: Vec<(String, String)>,
+        api_key: Option<String>,
+    },
+    Clock {
+        format: String,
+        timezone: String,
+    },
+    StaticText {
+        text: String,
+    },
 }
 
 #[derive(Debug, Clone)]
@@ -38,18 +49,28 @@ impl DataSource {
     pub fn validate(&self) -> Vec<DataSourceValidationError> {
         let mut errors = Vec::new();
 
-        let is_webhook = self.source_type == DataSourceType::Webhook;
-
-        if is_webhook {
-            if !self.poll_interval.is_zero() {
-                errors.push(DataSourceValidationError::PollIntervalNotAllowed);
+        match self.source_type {
+            DataSourceType::Webhook => {
+                if !self.poll_interval.is_zero() {
+                    errors.push(DataSourceValidationError::PollIntervalNotAllowed);
+                }
             }
-        } else {
-            if self.poll_interval.is_zero() {
-                errors.push(DataSourceValidationError::PollIntervalRequired);
+            DataSourceType::Clock | DataSourceType::StaticText => {
+                // Internal sources: poll_interval optional, no url needed
             }
-            if self.requires_url() && self.config.url.is_none() {
-                errors.push(DataSourceValidationError::UrlRequired);
+            _ => {
+                if self.poll_interval.is_zero() {
+                    errors.push(DataSourceValidationError::PollIntervalRequired);
+                }
+                if self.requires_url() {
+                    let has_url = matches!(
+                        &self.config,
+                        DataSourceConfig::External { url: Some(_), .. }
+                    );
+                    if !has_url {
+                        errors.push(DataSourceValidationError::UrlRequired);
+                    }
+                }
             }
         }
 

crates/domain/src/entities/widget_config.rs

@@ -35,6 +35,15 @@ impl WidgetConfig {
     }
 
     pub fn extract(&self, raw: &Value) -> WidgetState {
+        let has_mappings = self.mappings.iter().any(|m| !m.source_path.is_empty());
+        if !has_mappings {
+            let data = match raw {
+                Value::Object(map) => map.clone(),
+                _ => BTreeMap::new(),
+            };
+            return WidgetState { data, error: None };
+        }
+
         let budget = self.max_data_size as usize;
         let mut used = 0usize;
         let mut data = BTreeMap::new();