BoardState.CaptureSave/RestoreFromSave deep-copy every mutable field
(grid, pieces, demands, transformers, buffers, stock, campaign progress)
into a WorldSave slot. GameSim.QuickSave/QuickLoad expose slotted saves
and emit StateSavedEvent / StateRestoredEvent — the latter carries a
fresh BoardSnapshot so the presentation can rebuild board, pieces,
trajectories, objectives, stock, camera, and control bar in one pass.
F5/F9 trigger it in Main; harness gains quick_save/quick_load commands so
UI tests can checkpoint a scenario and resume without replaying from
scratch. Seven xUnit tests cover the roundtrip (including independence
from post-save mutations, campaign state, and multi-slot isolation).
