feat: adjust center group threshold to 250 for chat words

fix: scale down word cloud rendering for low absolute frequency words

fix: resolve mobile layout swipe and word cloud scaling

chore: replace Render reference with generic cloud server reference in loading screen

fix: use fully qualified API_BASE for avatar proxy requests

perf: optimize stats polling and add React ErrorBoundary for frontend crash fallback

feat: prepare transition to decoupled hosting (Render + Netlify + Supabase)