fix(client): address PR #70 review — event leak, quit flush, notification color

- input_mapper.gd: call set_input_as_handled() before early return on
  empty game_id so F5/F6 events don't propagate to other handlers
- session_manager.gd: defer scene change by one frame after buffering
  quit-save so SimBridge._process() flushes the outbound buffer
- monologue_display.gd: tag queued notifications with is_notification
  flag so drain path routes to _show_notification_line (correct color)
  instead of _show_line (lattice-profile fallback color)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/scripts/autoloads/input_mapper.gd

@@ -128,6 +128,7 @@ func _unhandled_input(event: InputEvent) -> void:
 		if action == Action.SAVE_GAME or action == Action.LOAD_GAME:
 			var game_id := GameState.current_game_id
 			if game_id.is_empty():
+				get_viewport().set_input_as_handled()
 				return  # No active session — ignore save/load
 			entry["action_data"] = {"path": "user://saves/" + game_id + "/quicksave.sav"}
 		input_queue.append(entry)