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/client-esp32/src/tasks/network.rs

@@ -1,12 +1,13 @@
 use std::sync::mpsc;
 use std::thread;
 use client_domain::NetworkPort;
-use protocol::{ServerMessage, decode_server_message};
+use protocol::decode_server_message;
+use super::RenderEvent;
 use crate::config::{NET_THREAD_STACK_SIZE, NET_POLL_INTERVAL, NET_RECONNECT_DELAY};
 use crate::adapters::network::Esp32Network;
 use log::*;
 
-pub fn spawn(server_addr: String, tx: mpsc::Sender<ServerMessage>) {
+pub fn spawn(server_addr: String, tx: mpsc::Sender<RenderEvent>) {
     thread::Builder::new()
         .stack_size(NET_THREAD_STACK_SIZE)
         .name("net".into())
@@ -14,16 +15,20 @@ pub fn spawn(server_addr: String, tx: mpsc::Sender<ServerMessage>) {
         .expect("failed to spawn network thread");
 }
 
-fn run(server_addr: String, tx: mpsc::Sender<ServerMessage>) {
+fn run(server_addr: String, tx: mpsc::Sender<RenderEvent>) {
     let mut net = Esp32Network::new();
 
     loop {
         if !net.is_connected() {
             info!("Connecting to server {server_addr}...");
             match net.connect(&server_addr) {
-                Ok(()) => info!("Server connected"),
+                Ok(()) => {
+                    info!("Server connected");
+                    let _ = tx.send(RenderEvent::ConnectionStatus(true));
+                }
                 Err(e) => {
                     error!("Connection failed: {e}, retrying...");
+                    let _ = tx.send(RenderEvent::ConnectionStatus(false));
                     thread::sleep(NET_RECONNECT_DELAY);
                     continue;
                 }
@@ -33,7 +38,7 @@ fn run(server_addr: String, tx: mpsc::Sender<ServerMessage>) {
         match net.receive() {
             Ok(Some(payload)) => {
                 match decode_server_message(&payload) {
-                    Ok(msg) => { let _ = tx.send(msg); }
+                    Ok(msg) => { let _ = tx.send(RenderEvent::Server(msg)); }
                     Err(e) => error!("Decode error: {e}"),
                 }
             }
@@ -43,6 +48,7 @@ fn run(server_addr: String, tx: mpsc::Sender<ServerMessage>) {
             Err(e) => {
                 error!("Receive error: {e}, reconnecting...");
                 let _ = net.disconnect();
+                let _ = tx.send(RenderEvent::ConnectionStatus(false));
                 thread::sleep(NET_RECONNECT_DELAY);
             }
         }