Save-detail nil-safety + font floor + stacked overflow

Legacy saves missing GameMode/PlayTime/TimeStamp crashed the whole save-menu frame (fields healGameData never heals).

• All three concat sites nil-guarded in both width calc and drawing (GameMode/TimeStamp '?', PlayTime defaults 0)
• Font shrink loop floored at 8px instead of collapsing to 1px
• Rows still too wide at the floor now stack each info line on its own centered row; screenshot budget accounts for the triple-height block

Fleet card: 2e85db