Remove external UI Avatars API dependency and use a static default avatar
URL instead. Simplifies avatar utility functions by eliminating dynamic
avatar generation.
Implement sensitive word filtering feature with configurable database and Redis
support. Add security enhancements including WebSocket origin validation, improved
password strength requirements, timing attack prevention, and production JWT secret
validation. Add batch operation validation limits and optimize user blocking
queries with subqueries.
BREAKING CHANGE: Password validation now requires minimum 8 characters with uppercase,
lowercase, and digit (was 6-50 characters without complexity requirements)
