Prevent UInt16 overflow when deleting WadTool state changes

[Copilot]

Deleting the first row in WadTool's Animation Editor state change grid could throw a System.OverflowException from DataGridView while rebinding cell values. The failure was caused by unsigned row-bound properties receiving transient invalid values during grid row removal.

• Use signed editing state in the grid

  • Changed FormStateChangesEditor's WadStateChangeRow numeric fields from ushort to int.
  • This keeps DataGridView editing/deletion in a signed domain and avoids the WinForms conversion path that overflowed on row deletion.

• Clamp only at persistence boundaries

  • Added centralized clamping when converting edited row values back into WadStateChange / WadAnimDispatch.
  • Stored wad data remains ushort-based; only the editor's in-memory row model changed.

• Keep related editor paths consistent

  • Updated blend field assignments and validation comments to match the new signed row model.
  • No behavior change to saved animation/state-change data beyond preventing the delete-time exception.

private class WadStateChangeRow
{
    public int StateId { get; set; }
    public int LowFrame { get; set; }
    public int HighFrame { get; set; }
    public int NextAnimation { get; set; }
    public int NextFrame { get; set; }
}

private static ushort ClampRowValue(int value)
{
    return (ushort)Math.Clamp(value, ushort.MinValue, ushort.MaxValue);
}

[Nickelony]

WinForms back at it again...