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_shaders.gd

@@ -0,0 +1,85 @@
+@tool
+extends SceneTree
+
+# One-shot migration tool: walk every resource that can carry a ShaderMaterial
+# (.material, .tres, .mesh, .scn, .gltf, .glb, .tscn) and fix Godot 3 -> 4
+# shader code in-place, saving where possible.
+#
+# Run with: godot --headless --script scripts/migrate_shaders.gd
+
+const REPLACEMENTS := [
+	["depth_draw_alpha_prepass", "depth_prepass_alpha"],
+	["hint_color", "source_color"],
+	["hint_albedo", "source_color"],
+	["hint_black_albedo", "source_color"],
+	["hint_white", ""],
+	["hint_black", ""],
+	["hint_aniso", "hint_anisotropy"],
+	["NORMALMAP", "NORMAL_MAP"],
+]
+
+const EXTENSIONS := [".material", ".tres", ".mesh"]
+
+func _init() -> void:
+	var fixed := 0
+	var checked := 0
+	for path in _find_resources("res://assets"):
+		checked += 1
+		var res = ResourceLoader.load(path, "", ResourceLoader.CACHE_MODE_IGNORE)
+		if res == null:
+			continue
+		var dirty := false
+		# Direct ShaderMaterial
+		if res is ShaderMaterial:
+			dirty = _fix_shader_material(res) or dirty
+		# ArrayMesh (surface materials embedded)
+		if res is ArrayMesh:
+			for surf in range(res.get_surface_count()):
+				var mat = res.surface_get_material(surf)
+				if mat is ShaderMaterial:
+					if _fix_shader_material(mat):
+						res.surface_set_material(surf, mat)
+						dirty = true
+		if dirty:
+			var err = ResourceSaver.save(res, path)
+			if err == OK:
+				fixed += 1
+				print("FIXED ", path)
+			else:
+				push_error("Failed to save " + path + " (err=" + str(err) + ")")
+	print("Done. checked=", checked, " fixed=", fixed)
+	quit()
+
+func _fix_shader_material(mat: ShaderMaterial) -> bool:
+	if mat.shader == null:
+		return false
+	var old_code: String = mat.shader.code
+	var new_code := old_code
+	for pair in REPLACEMENTS:
+		new_code = new_code.replace(pair[0], pair[1])
+	if new_code == old_code:
+		return false
+	mat.shader.code = new_code
+	return true
+
+func _find_resources(dir_path: String) -> 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 == "." or name == "..":
+			name = dir.get_next()
+			continue
+		var sub = dir_path + "/" + name
+		if dir.current_is_dir():
+			result.append_array(_find_resources(sub))
+		else:
+			for ext in EXTENSIONS:
+				if name.ends_with(ext):
+					result.append(sub)
+					break
+		name = dir.get_next()
+	return result