feat: add /chat/demo endpoint to power KaalChat widget with memory

feat: add XTTSv2 TTS endpoint + public demo chat with Amber voice, template-first responses, and Chronos memory consent storage

Rebrand to Kaal — rename from Chronos OS, add Logo component with serif seal design, swap all Hexagon icons for Logo

Fix: Resolve Cross-Origin Resource Sharing (CORS) pre-flight blocks for Vercel deployments via vercel.json and FastAPI router fixes

Diag: Add verbose logging and debug uvicorn CMD for HF deployment

Migrate Backend to Hugging Face Spaces (16GB RAM optimization)

Diag: Add timing logs to lifespan startup

Migrate: SQLite+ChromaDB → Neon PostgreSQL+pgvector (persistent cloud storage)

10x Code Quality: Fix crash bug, cache LLM singletons, optimize batch inserts, purge stale references

Initial commit for Chronos OS MVP