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/session/mod.rs

@@ -7,10 +7,11 @@
 //! - Input event handling
 
 use crate::capture::{self, Capturer, Display};
+use crate::chat::{ChatController, ChatMessage as ChatMsg};
 use crate::config::Config;
 use crate::encoder::{self, Encoder};
 use crate::input::InputController;
-use crate::proto::{Message, message};
+use crate::proto::{Message, message, ChatMessage};
 use crate::transport::WebSocketTransport;
 use crate::tray::{TrayController, TrayAction};
 use anyhow::Result;
@@ -148,8 +149,8 @@ impl SessionManager {
         Ok(())
     }
 
-    /// Run the session main loop with tray event processing
-    pub async fn run_with_tray(&mut self, tray: Option<&TrayController>) -> Result<()> {
+    /// Run the session main loop with tray and chat event processing
+    pub async fn run_with_tray(&mut self, tray: Option<&TrayController>, chat: Option<&ChatController>) -> Result<()> {
         if self.transport.is_none() {
             anyhow::bail!("Not connected");
         }
@@ -215,9 +216,38 @@ impl SessionManager {
             };
 
             for msg in messages {
+                // Handle chat messages specially
+                if let Some(message::Payload::ChatMessage(chat_msg)) = &msg.payload {
+                    if let Some(c) = chat {
+                        c.add_message(ChatMsg {
+                            id: chat_msg.id.clone(),
+                            sender: chat_msg.sender.clone(),
+                            content: chat_msg.content.clone(),
+                            timestamp: chat_msg.timestamp,
+                        });
+                    }
+                    continue; // Don't pass to handle_message
+                }
                 self.handle_message(&mut input, msg)?;
             }
 
+            // Check for outgoing chat messages from user
+            if let Some(c) = chat {
+                if let Some(outgoing) = c.poll_outgoing() {
+                    let chat_proto = ChatMessage {
+                        id: outgoing.id,
+                        sender: "client".to_string(),
+                        content: outgoing.content,
+                        timestamp: outgoing.timestamp,
+                    };
+                    let msg = Message {
+                        payload: Some(message::Payload::ChatMessage(chat_proto)),
+                    };
+                    let transport = self.transport.as_mut().unwrap();
+                    transport.send(msg).await?;
+                }
+            }
+
             // Capture and send frame if interval elapsed
             if last_frame_time.elapsed() >= frame_interval {
                 last_frame_time = Instant::now();