Co-op pass: host-disconnect handling, spectate, late-join wave sync

- Clients now handle the host closing the arena: bank winnings if
  still alive (retire), reset the HUD, and return to the camp menu
  instead of being stranded in a dead world
- Death in co-op offers Spectate when a teammate is still fighting:
  closes the results overlay and watches the run; the escape menu
  gains a "Back to Camp" option for dead spectators to leave later
- Late joiners receive the current wave number on connect so their
  HUD doesn't sit on "Prepare..." until the next wave starts

level/ui/scripts/run_results.gd

@@ -80,6 +80,15 @@ func _ready():
 
 	_add_spacer(vbox, 16)
 
+	# Spectate option - only when a teammate is still fighting
+	if _teammates_still_alive():
+		var spectate_button = Button.new()
+		spectate_button.text = "Spectate"
+		spectate_button.custom_minimum_size = Vector2(0, 44)
+		spectate_button.pressed.connect(_on_spectate_pressed)
+		vbox.add_child(spectate_button)
+		_add_spacer(vbox, 6)
+
 	# Return button
 	var return_button = Button.new()
 	return_button.text = "Return to Camp"
@@ -90,6 +99,25 @@ func _ready():
 	# Make sure the mouse is usable on the overlay
 	Input.mouse_mode = Input.MOUSE_MODE_VISIBLE
 
+## Any other living player in the arena?
+func _teammates_still_alive() -> bool:
+	if multiplayer.multiplayer_peer == null:
+		return false
+	var level = get_tree().get_current_scene()
+	if not level or not level.has_node("PlayersContainer"):
+		return false
+	var my_id = multiplayer.get_unique_id()
+	for p in level.get_node("PlayersContainer").get_children():
+		if p is Character and not p.is_dead and str(p.name).to_int() != my_id:
+			return true
+	return false
+
+## Close the overlay and watch the run play out (escape menu can leave later).
+## For the host this also keeps the server alive for everyone else.
+func _on_spectate_pressed():
+	Input.mouse_mode = Input.MOUSE_MODE_CAPTURED
+	queue_free()
+
 func _add_header(parent: Control, text: String):
 	var label = Label.new()
 	label.text = text