Add comprehensive message validation with three protection mechanisms:
1. Rate Limiting: 10 messages per minute per user
2. Duplicate Detection: Prevents sending identical messages within 1 minute
3. Profanity Filter: Blocks inappropriate language (English + Polish)
Implementation:
- New messageValidation.js middleware with validateMessage() function
- Integrated into both event chat and match chat handlers
- Uses bad-words library (v2.0.0 for CommonJS compatibility)
- In-memory tracking with automatic cleanup every 5 minutes
- User-friendly error messages for each validation type
Technical details:
- Rate limit: 10 msg/min sliding window
- Duplicate check: Last 5 messages within 60s window
- Profanity: bad-words + 11 Polish words
- Memory management: Periodic cleanup of expired data
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