Replace Event + GlobalAnimation autoloads with class_name + static funcs

Two of the five autoloads were stateless helper bundles, not the
persistent application-wide systems that the Godot 4 best-practice
guide reserves autoload slots for. Convert them to plain classes with
all-static methods so they no longer need a Node living under /root.

- scripts/Animation.gd -> scripts/game_animation.gd (renamed:
  conflict with the built-in Animation class; the autoload sidestepped
  it by being called GlobalAnimation). class_name GameAnimation,
  every helper static. The dissolve tween now captures its target
  material in a lambda closure, eliminating the current_material
  member that the autoload kept as shared mutable state.
- scripts/Event.gd -> scripts/event.gd, class_name Event, every
  handler static. Added Event.level_pressed(name) -> Callable for the
  one place ChooseScene needed dynamic lookup of a per-level handler
  (replaces the old _build_method('_on_' + name + '_pressed') +
  Callable(autoload, string) reflection trick with an explicit match).

Updated call sites:
- scripts/Global.gd: animation.connect('animation_started',
  Callable(Event, '...')) -> animation.animation_started.connect(
  Event._loading_is_started). Same for animation_finished.
- scenes/levels/Levels.gd: GlobalAnimation.* -> GameAnimation.*;
  Quit/TextureButton.connect('pressed', Callable(Event, '...')) ->
  pressed.connect(Event._on_main_scene_pressed).
- scenes/UI/choose_scenes/ChooseScene.gd: per-level button connects
  go through Event.level_pressed(); reset button's bound callable now
  reads Event._on_reset_level.bind(...); cleanup no longer relies on
  is_connected with an unbound Callable (which would never match a
  bound one anyway) -- iterates reset.pressed.get_connections()
  instead. Drop the now-dead _build_method helper.

Also: organise scripts/ by promoting the one-shot migration helpers
(migrate_shaders, migrate_misc, resave_scenes, devisualize_shaders,
find_visualshaders) into scripts/migration/. They are not part of
the runtime and should not be browsable next to the autoloads.

Autoload count goes 5 -> 3 (Loading, Global, Setting remain --
Setting will move to a Resource in a later refactor).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scenes/UI/choose_scenes/ChooseScene.gd

@@ -27,9 +27,6 @@ func _load_scene(p_name):
 func _build_path(p_name):
 	return "MarginContainer/" + p_name
 
-func _build_method(p_name):
-	return "_on_" + p_name.to_lower() + "_pressed"
-
 func _load_texture(thumbnail):
 	return load(thumbnail)
 
@@ -38,7 +35,9 @@ func _configure_select(level, node):
 	var thumbnail = get_node(node+"/MarginContainer/CenterAlign/MainButton/MarginStich/ThumbnailLevel")
 	
 	thumbnail.set_texture(_load_texture(level.thumbnail()))
-	selector.connect("pressed", Callable(Event, _build_method(level.name())))
+	var handler = Event.level_pressed(level.name())
+	if handler.is_valid():
+		selector.pressed.connect(handler)
 
 func configure_reset(level, node, index, animate):
 	var reset = get_node(node+"/MarginContainer/CenterAlign/MainButton/TabAlign/ButtonReset")
@@ -55,14 +54,14 @@ func _configure_reset_disable(animation, reset, animate = false):
 	
 	reset.set_disabled(true)
 	reset.set_default_cursor_shape(CURSOR_ARROW)
-	if reset.is_connected("pressed", Callable(Event, "_on_reset_level")):
-		reset.disconnect("pressed", Callable(Event, "_on_reset_level"))
+	for c in reset.pressed.get_connections():
+		reset.pressed.disconnect(c["callable"])
 
 func _configure_reset_enable(animation, reset, level, node, index):
 	animation.play_backwards("SlideReset")
 	reset.set_disabled(false)
 	reset.set_default_cursor_shape(CURSOR_POINTING_HAND)
-	reset.connect("pressed", Callable(Event, "_on_reset_level").bind(level, node, index, self))
+	reset.pressed.connect(Event._on_reset_level.bind(level, node, index, self))
 
 func configure_counter(level, node):
 	var count = get_node(node+"/MarginContainer/CenterAlign/MainButton/TabAlign/ButtonCount/MarginBottom/Label")