fix: power on GIP controllers

Send GIP_PWR_ON when a controller is identified, matching the upstream
gamepad probe before authentication and input initialization.

Co-Authored-By: openai/gpt-5.6-luna: matched controller power-up flow

src/app/api.cpp

@@ -173,8 +173,14 @@ auto controller_transport::set_encryption_key(
     return chip_.set_client_key(wcid_, key);
 }
 
-auto controller_listener::on_client_added(xone::gip::client&) -> void
+auto controller_listener::on_client_added(xone::gip::client& client) -> void
 {
+    if (auto err = client.set_power_mode(xone::gip::GIP_PWR_ON); err != 0) {
+        xone::log_msg(xone::log_level::warn,
+                      "api: controller power-on failed (%d)", err);
+        return;
+    }
+
     std::lock_guard<std::mutex> guard(dongle_.lock);
     controller_.gip_ready = true;
     xone::log_msg(xone::log_level::info,