security: implement rate limiting

[diiabblo]

Description

Add rate limiting to prevent abuse and ensure fair usage.

Areas to Cover

• API rate limiting
• Smart contract call throttling
• Wallet connection attempts
• Question submission frequency

Implementation

• Redis-based rate limiting
• IP-based restrictions
• Wallet address tracking
• Progressive penalties

Acceptance Criteria

• Prevent spam attacks
• Fair usage for all players
• Graceful error handling