Fixed Expedition saves disappearing from Continue

I fixed Expedition saves being checked against the smaller map active at startup. Valid scouting destinations could fail that check and make the save disappear from the load list.

Validation now uses the Expedition field definition independently of the current world. Preserved saves round-trip with their progress intact, and the native Save, Main Menu and Continue flow has been checked. The accompanying demonstration uses a fresh isolated campaign; it does not expose the creator's recovered save.

“Expedition scouting destinations are now validated against their own field, so valid progress remains available at startup.”