Fix TUI: show GyanDoot banner + wire live agent responses

Two bugs fixed:

1. Banner not shown: TUI default output was a plain welcome text
   instead of the actual GyanDoot banner. Fixed by using
   banner::banner_plain() as initial TUI output content.

2. No agent responses: TUI was a standalone shell with no connection
   to the agent loop. Now uses mpsc channels:
   - user_tx: TUI → agent (user sends messages)
   - event_rx: agent → TUI (agent sends responses + telemetry)
   - TuiEvent::Response / Status / Telemetry enum for structured
     communication
   - tokio::spawn runs agent in background processing messages
   - poll_events() in render loop drains channel every frame tick

Also updated cmd_tui() in main to create channels + spawn agent.

src/main.rs

@@ -551,10 +551,54 @@ async fn cmd_setup() -> anyhow::Result<()> {
     Ok(())
 }
 
-/// Launch the TUI interface
+/// Launch the TUI interface with a live agent loop
 async fn cmd_tui() -> anyhow::Result<()> {
-    tracing::info!("Launching TUI");
-    gyandoot_tui::tui::run_tui()?;
+    tracing::info!("Launching TUI with live agent");
+
+    // Print banner to stdout too (for logs/terminal buffer)
+    gyandoot_tui::banner::print_banner();
+
+    // Load agent config
+    let config = load_agent_config();
+
+    // Create channels for TUI ↔ agent communication
+    let (user_tx, mut user_rx) = tokio::sync::mpsc::channel::<String>(256);
+    let (event_tx, event_rx) = tokio::sync::mpsc::channel::<gyandoot_tui::tui::TuiEvent>(256);
+
+    // Spawn agent task
+    let agent = gyandoot_agent::agent_loop::AgentLoop::new(config);
+    let agent_event_tx = event_tx.clone();
+    tokio::spawn(async move {
+        // Send initial telemetry
+        let _ = agent_event_tx.send(gyandoot_tui::tui::TuiEvent::Status("AGENT READY".to_string())).await;
+
+        // Process messages from TUI
+        while let Some(user_msg) = user_rx.recv().await {
+            let _ = agent_event_tx.send(gyandoot_tui::tui::TuiEvent::Status("PROCESSING...".to_string())).await;
+            match agent.run_conversation(&user_msg).await {
+                Ok(output) => {
+                    let _ = agent_event_tx.send(gyandoot_tui::tui::TuiEvent::Telemetry {
+                        provider: "—".to_string(),  // populated from config
+                        model: "—".to_string(),
+                        total_tokens: 0,
+                        max_tokens: 4096,
+                        msg_count: 0,
+                    }).await;
+                    let _ = agent_event_tx.send(gyandoot_tui::tui::TuiEvent::Response(output.text)).await;
+                }
+                Err(e) => {
+                    let _ = agent_event_tx.send(gyandoot_tui::tui::TuiEvent::Status(
+                        format!("ERROR: {}", e)
+                    )).await;
+                }
+            }
+        }
+    });
+
+    // Run TUI (this blocks until user quits)
+    gyandoot_tui::tui::run_tui(event_rx, user_tx).await?;
+
+    tracing::info!("TUI closed");
     Ok(())
 }