Add blood decals, gore, mobile HUD, web start gate + touch/perf tests

Remove tools/fstest.html scratch page used to probe browser
fullscreen/orientation APIs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EznnY8rH2dXhtono1kwsXg

levels/game_shell.gd

@@ -30,6 +30,9 @@ func load_active_level() -> void:
 	var module := level.level_scene.instantiate()
 	_tag_environment_for_corpses(module)
 	_level_root.add_child(module)
+	# A fresh blood-splat pool for this level, alongside the module under LevelRoot so it's
+	# torn down with everything else on the next load — stains never leak into the next fight.
+	_level_root.add_child(preload("res://blood_decals.gd").new())
 
 
 ## Ground and walls stay on WORLD so the bull and live matadors collide with them; here