[codex] Add Tetris touch gestures

[JeremyDemers]

What changed

• add tap-to-rotate controls across the Tetris board
• add horizontal drag movement with cell-sized stepping
• add downward drag and swipe-to-drop behavior
• show touch-specific control hints on coarse-pointer devices
• preserve keyboard, mouse, and on-screen button controls

Why

Tetris did not have practical controls on iPhone. These gestures make the game playable with familiar mobile interactions while treating the whole board as the touch target, so players do not need to chase the falling piece with a finger.

Validation

• lint passed
• production build passed
• mobile browser test confirmed touch hints, horizontal movement, and downward drop
• git diff --check passed