Add a debug-only level skip overlay so testing level 3 does not require beating levels 1 and 2

Registered as an autoload so every scene gets it for free. Top-right shows a row of buttons generated from the levels array (main, level2, level3) plus keyboard shortcuts 1/2/3, and it runs with PROCESS_MODE_ALWAYS at layer 30 so it still works while the tree is paused on a death or level-clear screen. Hidden in exported release builds, same rule as the debug flight.

scenes/level_skip.tscn

@@ -0,0 +1,29 @@
+[gd_scene load_steps=3 format=3]
+
+[ext_resource type="Script" path="res://scripts/level_skip.gd" id="1_skip"]
+
+[sub_resource type="SystemFont" id="SystemFont_cjk"]
+font_names = PackedStringArray("Microsoft YaHei UI", "Microsoft YaHei", "SimHei", "Noto Sans CJK SC", "sans-serif")
+
+[node name="LevelSkip" type="CanvasLayer"]
+process_mode = 3
+layer = 30
+script = ExtResource("1_skip")
+
+[node name="Buttons" type="HBoxContainer" parent="."]
+anchor_left = 1.0
+anchor_right = 1.0
+offset_left = -130.0
+offset_top = 6.0
+offset_right = -6.0
+offset_bottom = 32.0
+theme_override_constants/separation = 4
+
+[node name="Hint" type="Label" parent="Buttons"]
+theme_override_colors/font_color = Color(1, 1, 1, 0.85)
+theme_override_colors/font_outline_color = Color(0, 0, 0, 0.8)
+theme_override_constants/outline_size = 3
+theme_override_fonts/font = SubResource("SystemFont_cjk")
+theme_override_font_sizes/font_size = 11
+text = "跳关"
+vertical_alignment = 1