Support “Holey Y” boards (cells that cannot be played)

[UO300731]

Requirements:

• The board layout must allow defining blocked cells.
• Blocked cells:
  • Cannot be clicked or selected.
  • Must be visually distinguishable in the UI.
• Game logic must ignore blocked cells:
  • They cannot be filled.
  • They should not affect winner detection incorrectly.
• Board generation should support:
  • Either predefined patterns or configurable holes.

Acceptance criteria:

• Users cannot place pieces on blocked cells.
• Blocked cells are clearly visible in the UI.
• Winner detection still works correctly with holes.
• No crashes or inconsistencies in gameplay.