bug: Double undo snapshot pushed when executeAndRecalculate calls Game.move

[nodots]

Problem

Both Game.move() (line ~959) and Game.executeAndRecalculate() (line ~1395) push pre-move snapshots onto activePlay.undo.frames. Since executeAndRecalculate() calls Game.move() internally (line ~1409), two snapshots are pushed for a single logical move when the move is initiated through executeAndRecalculate.

This means:

• Calling undoLastInActivePlay() once only pops the inner snapshot — the game state is still post-move
• Users/robots must call undo twice to revert a single move made through executeAndRecalculate
• The undo stack grows at 2x the expected rate, wasting memory

Reproduction

1. Call Game.executeAndRecalculate(game, originId) to make a move
2. Inspect game.activePlay.undo.frames.length — it has 2 entries instead of 1
3. Call Game.undoLastInActivePlay(game) — the board state doesn't match the pre-move state

Affected code

• src/Game/index.ts — Game.move() snapshot push (~line 959)
• src/Game/index.ts — Game.executeAndRecalculate() snapshot push (~line 1395)

Implementation Plan

1. Remove the snapshot push from Game.executeAndRecalculate() (lines ~1394-1407) — let Game.move() be the single source of truth for undo snapshots
2. Add a unit test that verifies: after calling executeAndRecalculate once, undo.frames.length === 1
3. Add a test that verifies: calling undoLastInActivePlay after a single executeAndRecalculate move restores the exact pre-move board state
4. Verify switchDice gating still works correctly with single-snapshot undo stack

Files to modify

• src/Game/index.ts — remove duplicate snapshot in executeAndRecalculate
• src/Game/__tests__/undo-stack.test.ts — new test file