Add tetris game implementation

[Copilot]

Implements a complete, playable tetris game as requested.

Implementation

• Single self-contained HTML file (tetris.html) with embedded CSS and JavaScript
• Core mechanics: All 7 tetromino shapes, rotation, collision detection, line clearing, scoring, progressive difficulty
• UI: Canvas-based game board with real-time score/level/lines display, next piece preview, keyboard controls (arrows, space, P)

Technical Details

• 12x20 game board rendered on HTML5 canvas at 20px blocks
• Game loop using requestAnimationFrame with configurable drop intervals (1000ms base, decreases 100ms per level)
• Scoring: 40/100/300/1200 points for 1/2/3/4 lines cleared (multiplied by level)
• No external dependencies or network requests

Screenshot

The game shows multiple pieces stacked on the board with proper collision detection, a purple T-piece in the next piece preview, and real-time score tracking at 54 points.

Original prompt

tetris game

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