feat: add Aura Investment Product Engine project brief
- Create comprehensive project brief for Investment Product Engine
- Consolidate context from Aura platform, Earn product, and engine specs
- Define problem statement, target users, and key requirements
- Outline integration needs with Hex Safe, HollaEx, and exchanges
- Document success metrics and MVP scope
- Establish foundation for detailed PRD creation
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Co-Authored-By: Claude <noreply@anthropic.com>
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