fix: suppress 3 benign startup warnings on Windows client

- Create missing server/plugins/ dir with .gdignore (stops PluginManager warning)

- Create config/default_server_config.cfg (stops ServerConfig error)

- Reorder light look_at after add_child (stops 'not in tree' warning)

- Switch rendering_method from opengl3 to forward_plus (RTX 2080 Vulkan works fine; gray screen was server-scene issue not OpenGL)

scripts/network/client_main.gd

@@ -70,8 +70,8 @@ func _setup_scene() -> void:
 	light.light_energy = 1.0
 	light.shadow_enabled = true
 	light.position = Vector3(10, 20, 10)
-	light.look_at(Vector3.ZERO)
 	add_child(light)
+	light.look_at(Vector3.ZERO)
 
 # ---------------------------------------------------------------------------
 # Player replication handlers (called when server broadcasts via RPC)