Add ModOptions unique to disable undo

[Fanfblrik]

Summary

• Adds ModOptions unique Disable undo.
• Disables the in-game Undo button and undo checkpoints.
• In online multiplayer, also closes the rejoin/reload bypass:
  • Debounced mid-turn upload to the MP server after moves, combat, and unit actions
  • Always download from the server when opening/resuming (never prefer a local mid-turn copy that only matches turn/player)

Example ModOptions.json

{
  "uniques": [
    "Disable undo"
  ]
}

Motivation

Players can undo scout/combat outcomes via Undo, or by rejoining an online game (server usually only updates on end turn). This unique closes both paths for competitive multiplayer.

Test plan

• Enable an extension mod with Disable undo
• Offline/single-player: Undo button never appears after a move
• Online MP + unique: move a unit → wait ~2s → rejoin from multiplayer list → unit is still on the new tile
• Online MP + unique: Resume/autoload uses server state, not a stale local autosave
• Without the mod → vanilla Undo / end-turn-only upload behavior

[github-actions]

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[github-actions]

Conflicts have been resolved.