Accept story 40: MCP Server Obeys STORYKIT_PORT

Agent worktrees now get a .mcp.json written with the correct port from
the running server. AgentPool receives the port at construction and
passes it through to create_worktree, which writes .mcp.json on both
new creation and reuse.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/main.rs

@@ -50,7 +50,8 @@ async fn main() -> Result<(), std::io::Error> {
         JsonFileStore::from_path(PathBuf::from("store.json")).map_err(std::io::Error::other)?,
     );
     let workflow = Arc::new(std::sync::Mutex::new(WorkflowState::default()));
-    let agents = Arc::new(AgentPool::new());
+    let port = resolve_port();
+    let agents = Arc::new(AgentPool::new(port));
 
     let ctx = AppContext {
         state: app_state,
@@ -60,8 +61,6 @@ async fn main() -> Result<(), std::io::Error> {
     };
 
     let app = build_routes(ctx);
-
-    let port = resolve_port();
     let addr = format!("127.0.0.1:{port}");
 
     println!(