M5: rmcp stdio client and tool adapters

Adds an rmcp-based stdio MCP client in harness-mcp plus adapters exposing a configured server's tools as namespaced harness-tools, with an echo-server fixture and integration test, and wiring through harness-app.

crates/harness-tui/src/app.rs

@@ -31,7 +31,7 @@ pub struct App {
 
 impl App {
     pub async fn new(cwd: PathBuf) -> anyhow::Result<Self> {
-        let engine = EngineHandle::init(cwd)?;
+        let engine = EngineHandle::init(cwd).await?;
         let bus_rx = engine.bus().subscribe();
 
         let config = engine.config();

crates/harness-tui/src/main.rs

@@ -50,7 +50,7 @@ async fn run_headless(args: &[String]) -> i32 {
         }
     };
 
-    let app = match harness_app::App::init(cwd) {
+    let app = match harness_app::App::init(cwd).await {
         Ok(app) => app,
         Err(e) => {
             eprintln!("error: {e}");