[WIP] Perform comprehensive code quality assessment

[Copilot]

• Fix FlappyGame bugs:
  • Scoring never fires (exact equality skips due to 6px steps)
  • startGame button shows "Restart" but does nothing when gameOver=true
  • Keyboard handler doesn't start game from initial state via Space/Enter
  • handleFlap allows flapping before game starts
  • Replace interval-per-tick anti-pattern with velocityRef
• Fix TetrisGame speed progression (adding level to game loop deps so speed increases work)
• Fix SnakeGame code duplication (4 copies of debounce logic)
• Export pure functions from Game2048 and TetrisGame for testability
• Add Next Piece preview display to TetrisGame (state exists but is never rendered)
• Add ErrorBoundary component and wire it into App.tsx
• Add unit tests for pure game logic functions (Game2048, TetrisGame)
• Add component smoke tests (render without crash)
• Verify lint, build, and tests pass

Original prompt

perform a comprehensive code quality assessment

The user has attached the following file paths as relevant context:

• .github\copilot-instructions.md

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