IRC: edit server settings as a draft, applied under the service lock

The IRC App edited the live config while the IRC task could be reading
it to connect. The App now edits a copy; applyConfig() validates it and
swaps it in under the lock, and the task connects from a snapshot.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

src/apps/irc_app.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <memory>
 #include <string>
 
 #include "app.h"
@@ -50,6 +51,7 @@ class IrcApp : public App {
     ListModel fields_{theme::kContent.h / theme::kLineHeight};
     bool editing_ = false;
     LineEditor fieldEditor_{63};
+    std::unique_ptr<IrcConfig> draft_;  // the settings being edited, applied on Save
 };
 
 }  // namespace roro