Fix combat-sandbox.html DOM access errors from sandboxMode

[Copilot]

combat-sandbox.html broke after sandboxMode implementation. TypeError occurred when UISystem.updateHUD() attempted to set textContent on null DOM elements that don't exist in the sandbox environment.

Changes

Combat Sandbox Fix

• Override all UI methods that access DOM after game instantiation
• Methods disabled: updateHUD, showScreen, showWaveAnnouncement, showLevelUp, showGameOver
• Prevents TypeError: Cannot set properties of null while maintaining sandbox functionality

Obsolete File Cleanup

• Reverted combat-sandbox-pro.html to original state (marked obsolete per maintainer)

Technical Details

sandboxMode disables ui.update() at engine level, but other UI methods remain callable. When invoked by game systems, they fail accessing non-existent DOM elements:

// After: explicit method stubs prevent DOM access
if (game.systems.ui) {
    game.systems.ui.updateHUD = function() {};
    game.systems.ui.showScreen = function() {};
    game.systems.ui.showWaveAnnouncement = function() {};
    game.systems.ui.showLevelUp = function() {};
    game.systems.ui.showGameOver = function() {};
    console.log('[Combat Sandbox] UI methods overridden to prevent DOM errors');
}

Result

Combat sandbox fully operational:

• Player/enemy spawning ✓
• Weapon systems ✓
• Defense calculations ✓
• No console errors ✓

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