Add chat functionality between technician and client

- Add ChatMessage to protobuf definitions
- Server relays chat messages between agent and viewer
- Agent chat module shows messages via MessageBox
- Dashboard chat modal with WebSocket connection
- Simplified protobuf encoder/decoder in JavaScript

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

agent/src/main.rs

@@ -9,6 +9,7 @@
 //! for a one-time support session.
 
 mod capture;
+mod chat;
 mod config;
 mod encoder;
 mod input;
@@ -198,6 +199,12 @@ async fn run_agent(config: config::Config) -> Result<()> {
         }
     };
 
+    // Create chat controller
+    let chat_ctrl = chat::ChatController::new();
+    if chat_ctrl.is_some() {
+        info!("Chat controller created");
+    }
+
     // Connect to server and run main loop
     loop {
         info!("Connecting to server...");
@@ -219,8 +226,8 @@ async fn run_agent(config: config::Config) -> Result<()> {
                     t.update_status("Status: Connected");
                 }
 
-                // Run session until disconnect, passing tray for event processing
-                if let Err(e) = session.run_with_tray(tray.as_ref()).await {
+                // Run session until disconnect, passing tray and chat for event processing
+                if let Err(e) = session.run_with_tray(tray.as_ref(), chat_ctrl.as_ref()).await {
                     let error_msg = e.to_string();
 
                     // Check if this is a user-initiated exit