Add progressive puzzle mode alongside the existing sandbox:
- 8 levels from basic gates to 2-bit adder
- Truth table verification with pass/fail feedback
- Gate restrictions per level
- Custom components system (save circuits as reusable chips)
- Save/load circuits as JSON
- Level selection sidebar with difficulty ratings
- Mode toggle: Sandbox (free play) vs Puzzle (guided levels)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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