Chess

Make a complete chess game. You play white against a computer playing black. Full legal rules: all piece moves, castling both sides with all conditions, en passant, pawn promotion (choose piece, default queen), check, checkmate, stalemate, draw by insufficient material and by the fifty-move rule. Highlight legal moves and the last move, show a check warning, captured pieces tray, move list in algebraic notation. Computer: alpha-beta minimax with material plus piece-square tables and quiescence search, Easy (depth 1 with randomness), Normal (depth 3), Hard (depth 4) toggle, run the search in small time slices or a Worker built from a Blob so the UI never freezes. Draw pieces with canvas using the Unicode chess glyphs (U+2654 to U+265F, filled glyphs for both sides, colour them ivory and charcoal with an outline). Undo takes back your last move and the reply. Board flips are not needed.