Fixed dataset validation

- Added strict dataset validation - loadGameData() now validates full structure, not just top-level shape.

- It only keeps entries where: - base is a non-empty string - matches is an array with valid objects - each match has non-empty string partner and compound

• Invalid entries are dropped safely and counted with a console warning.

Round-transition race prevention

• Added an isTransitioning lock to block actions during round changes.
• Added setControlsDisabled() to disable/enable input + action buttons during transitions.

- skipRound() now: - ignores re-clicks while transitioning - disables controls during the 700ms reveal window - updates round UI immediately after increment

- nextRound() now: - ignores rapid repeated clicks while transitioning - prevents round inflation from button spam