Connect Four

# Connect Four PRD

## Overview
Build a classic Connect Four game with a two-player mode, an AI opponent with difficulty levels, drop animations, win detection, and move history.

## Requirements
- Standard 7-column by 6-row grid
- Two-player mode with alternating red and yellow turns
- Drop piece animation that falls from the top of the column
- Win detection for horizontal, vertical, and both diagonal directions
- Draw detection when the board is completely full
- Highlight the winning four pieces visually
- AI opponent with difficulty levels: random moves and smart minimax
- Column hover preview showing a ghost piece before dropping
- Current player indicator display
- Move history and log showing each turn
- Undo last move functionality
- New game button to reset the board
- Win, loss, and draw counter persisted to localStorage
- Responsive layout that works on different screen sizes
- Keyboard support: keys 1-7 to select column, Enter to drop
- Board full animation when game ends in a draw

## Tech Stack
- JavaScript or any frontend framework
- CSS for animations and grid layout
- No game libraries

## Scoring Criteria
- **Functional (40%)**: Core gameplay works, win/draw detection correct, AI opponent functions
- **Quality (20%)**: Smooth drop animations, clean code, no edge case bugs
- **Fidelity (25%)**: All features present including AI levels, undo, move history, and keyboard support
- **Speed (15%)**: Time bonus