- Created comprehensive sanitization utility functions
- SanitizeInput, SanitizeText, SanitizeHTML, SanitizeURL, SanitizeEmail, SanitizeUsername
- Applied sanitization to profile handler (username, bio, names, search)
- Applied sanitization to social posts content
- Applied sanitization to comment content
- Applied sanitization to playlist titles and descriptions
- All functions prevent XSS via HTML escaping and remove dangerous URL schemes
- Removes control characters and limits input length to prevent DoS
