Added durable saves, quick items, and Alt-Drive movement

The save system now writes alternating durable generations and can recover from an interrupted or damaged write. Browser saves can also be exported and imported between sessions.

I added a quick-item bar for tools and supplies used repeatedly in the field. Important gear no longer has to be found through the full codex every time.

“A persistent survival game has to protect the time the player has already put into the wasteland.”

Holding Alt switches to direct movement, letting the selected survivor walk with the keyboard while the normal point-and-click command style remains available.

Together these changes make long Survival sessions safer to keep and less cumbersome to operate.