perf(daemon): skip the UI-thread datadir lock wait

Starting the daemon polls for an already-running node holding the
datadir, sleeping up to three 100 ms intervals to let a shutting-down
node clear out. When a start runs on the UI thread, that is up to 300 ms
of blocking sleep on the render thread.

- The lock-wait poll count is now a parameter. A start invoked on the UI
  thread passes 0, which does a single check and never sleeps; every
  other caller keeps the three-poll wait. The default is unchanged, so
  background starts behave exactly as before.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app.cpp

@@ -5975,7 +5975,8 @@ bool App::startEmbeddedDaemon()
 
     // Only a process we actually launched starts a new story: a start that finds a node already running (and
     // launches nothing) must not wipe what the tracker knows about that node from its debug.log.
-    const bool launched = daemon_controller_->start(settings_.get());
+    const bool launched = daemon_controller_->start(
+        settings_.get(), std::this_thread::get_id() == ui_thread_id_ ? 0 : daemon::EmbeddedDaemon::kDatadirLockWaitMaxPolls);
     if (launched) resetDaemonBusy();   // a new process: whatever the last one was doing is over
     return launched;
 }