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>

scripts/migration/migrate_misc.gd

@@ -0,0 +1,52 @@
+@tool
+extends SceneTree
+
+# One-shot cleanup:
+#  1. Reset VisualShader.graph_offset to default on every .material so the
+#     deprecated property no longer triggers a warning at load.
+#  2. Re-save every .mesh whose surface format is the old (Godot 3) variant
+#     so Godot 4 stops nagging.
+
+func _init() -> void:
+	var changed := 0
+
+	for path in _find_resources("res://assets", [".material", ".tres"]):
+		var res = ResourceLoader.load(path, "", ResourceLoader.CACHE_MODE_IGNORE)
+		if res is ShaderMaterial and res.shader is VisualShader:
+			var vs: VisualShader = res.shader
+			if vs.graph_offset != Vector2.ZERO:
+				vs.graph_offset = Vector2.ZERO
+				if ResourceSaver.save(res, path) == OK:
+					changed += 1
+					print("CLEARED graph_offset on ", path)
+
+	for path in _find_resources("res://assets", [".mesh"]):
+		var mesh = ResourceLoader.load(path, "", ResourceLoader.CACHE_MODE_IGNORE)
+		if mesh is ArrayMesh:
+			# Just re-saving rewrites the file using the current surface format.
+			if ResourceSaver.save(mesh, path) == OK:
+				changed += 1
+				print("RESAVED mesh ", path)
+
+	print("Done. changed=", changed)
+	quit()
+
+func _find_resources(dir_path: String, exts: Array) -> Array:
+	var result := []
+	var dir = DirAccess.open(dir_path)
+	if dir == null:
+		return result
+	dir.list_dir_begin()
+	var name = dir.get_next()
+	while name != "":
+		if name != "." and name != "..":
+			var sub = dir_path + "/" + name
+			if dir.current_is_dir():
+				result.append_array(_find_resources(sub, exts))
+			else:
+				for ext in exts:
+					if name.ends_with(ext):
+						result.append(sub)
+						break
+		name = dir.get_next()
+	return result