FloorGenerator

Procedural generator that builds one tower floor together with the initial GameSession snapshot for that level.

==== Overview ====

• Shuffle room names and arrange them in a matrixRooms grid (rows × columns) so the dungeon is always rectangular.
• Create every Room with random padding so shapes vary between runs.
• Populate rooms (except the spawn room) with enemies and items whose number scales with difficulty.
• Insert a Sign in the spawn room and an Exit Door in the last room to let the player advance to the next floor.
• Return a fully initialised GameSession that already contains one entry in the undo history (GameSession.init).